Patent Publication Number: US-2011076293-A1

Title: Triptolide derivatives for modulation of apoptosis and immunosuppression

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of currently pending U.S. application Ser. No. 10/478,777, a 35 U.S.C. §371 National Stage of International Application No. PCT/US03/17177, filed 29 May 2003, which claims the benefit under 35 U.S.C. §119(e) of Provisional Application No. 60/384,480, filed 31 May 2002, the contents of each of which are expressly incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to prodrugs useful as immunosuppressive, anti-inflammatory and anticancer agents, and methods of their use. The compounds have good aqueous solubility and convert to biologically active compounds in vivo, at a rate which can be modulated by varying the substitution on the prodrug. 
     REFERENCES 
     
         
         Bagshawe, K. D. Antibody directed enzymes revive anti-cancer prodrugs concept.  Br J Cancer  56:531-532 (1987). 
         Bagshawe, K. D. Antibody-directed enzyme prodrug therapy (ADEPT).  Adv Pharmacol.  24:99-121 (1993). 
         Bagshawe, K. D, Springer, C. J., Searle, F., Antoniw, P., Sharma, S. K., Melton, R. G., Sherwood R F. A cytotoxic agent can be generated selectively at cancer sites.  Br J Cancer  58:700-703 (1988). 
         Bagshawe, K. D. Towards generating cytotoxic agents at cancer sites.  Br J Cancer  60:275-281 (1989). 
         Boyd, G. V. and Heatherington, K.,  J. Chem. Soc. Perkin I  2523-2531 (1973). 
         Ferrier, R. J., in C ARBOHYDRATE  C HEMISTRY , Kennedy, J. F., Ed., Clarendon Press, Oxford (1990). 
         Garver, L. C. et al.,  J. Am. Chem. Soc.  104:867 (1982). 
         Gleichmann, E. et al.,  Immunol. Today  5:324 (1984). 
         Hormi, O. E. O. and Nasman, J. H.,  Syn. Commun.  16:69 (1986). 
         Kocienski, P. J., P ROTECTING  G ROUPS , Georg Thieme Verlag, Stuttgart (1994). 
         Korngold, R. and Sprent, J.,  J. Exp. Med.  148:1687 (1978). 
         Kupchan, S. M. et al.,  J. Am. Chem. Soc.  94:7194 (1972). 
         Kupchan, S. M. et al., U.S. Pat. No. 3,005,108 (1977). 
         Lipsky, P. E. et al., U.S. Pat. No. 5,294,443 (1994). 
         Ma, P-C. et al.,  J. Chin. Pharm. Sci.  1:12 (1992). 
         Mori, S. et al.,  Tetrahedron  47(27):5051-5070 (1991). 
         Morris, R. E.,  Transplant Proc.  23(6):2722-2724 (1991). 
         Morris, R. E. et al.,  Transplant Proc.  23(1):238-240 (1991). 
         Murase, N. et al.,  Transplantation  55:701 (1993). 
         Ono and Lindsey,  J. Thor. Cardiovasc. Surg.  57(2):225-29 (1969). 
         Pu, L. et al.,  Zhongguo Yaoli Xuebao  11:76 (1990). 
         Wang, J. and Morris, R. E.,  Transplantation Proc.  23:699 (1991). 
         Wentworth. P., Datta, A., Blakey, D., Boyle, T., Partridge, L. J., Blackburn, G. M.  Proc. Natl. Acad. Sci. USA  93:799-803 (1996). 
         Yu et al.,  Acta Pharmaceutica Sinica  27(11):830-836 (1992). 
         Zheng, J. et al.,  Zhongguo Yixue Kexueyuan Xuebao  13:391 (1991). 
         Zheng, J. et al.,  Zhongguo Yixue Kexueyuan Xuebao  16:24 (1994). 
       
    
     BACKGROUND OF THE INVENTION 
     Immunosuppressive agents are widely used in the treatment of autoimmune disease and in treating or preventing transplantation rejection, including the treatment of graft-versus-host disease (GVHD), a condition in which transplanted marrow cells attack the recipient&#39;s cells. Common immunosuppressive agents include azathioprine, corticosteroids, cyclophosphamide, methotrexate, 6-mercaptopurine, vincristine, and cyclosporin A. In general, none of these drugs are completely effective, and most are limited by severe toxicity. For example, cyclosporin A, a widely used agent, is significantly toxic to the kidney. In addition, doses needed for effective treatment may increase the patient&#39;s susceptibility to infection by a variety of opportunistic invaders. 
     A number of compounds derived from the Chinese medicinal plant  Tripterygium wilfordii  (TW) have been identified as having immunosuppressive activity, e.g. in the treatment of autoimmune disease, and in treating or preventing transplantation rejection, including the treatment of graft-versus-host disease (GVHD), a condition in which transplanted marrow cells attack the recipient&#39;s cells. See, for example, coowned U.S. Pat. No. 6,150,539 (Triptolide prodrugs having high aqueous solubility), U.S. Pat. No. 5,962,516 (Immunosuppressive compounds and methods), U.S. Pat. No. 5,843,452 (Immunotherapy composition and method), U.S. Pat. No. 5,759,550 (Method for suppressing xenograft rejection), U.S. Pat. No. 5,663,335 (Immunosuppressive compounds and methods), and U.S. Pat. No. 5,648,376 (Immunosuppressant diterpene compound), all of which are incorporated herein by reference, and references cited therein. Such compounds have also been reported to show anticancer activity. See, for example, Kupchan et al., 1972, 1977, cited above, as well as co-owned PCT Publication No. WO 02/56835, which is incorporated herein by reference. 
     The administration and therapeutic effectiveness of these compounds have been limited, however, by their low water solubility. This problem has been addressed by formulating the compounds in mixtures of ethanol and polyethoxylated castor oil (e.g., “CREMOPHOR EL™”), allowing subsequent dilution in saline for intravenous administration. However, such formulations have suffered from high toxicity, due to the high concentration of solubilizing agent required to dissolve these compounds. For example, the ratio of solubilizing agent (ethanol plus “CREMOPHOR EL™”) to triptolide in such formulations is typically on the order of 1000:1 or greater, due to the poor solubility of triptolide (Morris, 1991; Morris et al., 1991). Standardization of dosage amounts is also more problematic with a suspension than with a solution. 
     It is therefore desirable to provide immunosuppressive compounds having comparatively low toxicity and improved water solubility. It is also desirable to provide prodrug compounds which are convertible to an immunosuppressive form in vivo at a rate which can be controlled by selection of substituents on the prodrug. 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention provides a method of inducing cell death, as in treatment of cancer, particularly in treatment of treatment of colon cancer, breast cancer, lung cancer, or prostate cancer. In another aspect, the invention provides a method of effecting immunosuppression, as in inhibition of transplant rejection, prevention or treatment of graft-versus-host disease, or treatment of an autoimmune disease. In accordance with the invention, a subject in need of such treatment is treated with an effective amount of a triptolide prodrug, or a pharmaceutically acceptable salt thereof, having the structure I, below, in a pharmaceutically acceptable vehicle. 
     
       
         
         
             
             
         
       
     
     In the structure I, the variables are defined as follows: 
     X 1  is OH or OR 1 , and X 2  and X 3  are independently OH, OR 1  or H, with the proviso that at least one of X 1 , X 2  and X 3  is OR 1 , and at least one of X 2  and X 3  is H; and 
     OR 1  is O—(C═O)—Z, where Z is selected from the group consisting of: —OR 2 , —O—Y—(C═O)—OR 3 , —O—Y—NR 4 R 5 , —NR 4 R 5 , —NR 3 —Y—(C═O)—OR 3 , and —NR 3 —Y—NR 4 N 5 ; 
     wherein 
     Y is a divalent alkyl, alkenyl or alkynyl group having up to six carbon atoms; 
     R 2  is selected from alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aryl, aralkyl, hydroxyalkyl, alkoxyalkyl, aryloxyalkyl, and acyloxyalkyl; 
     each R 3  is independently selected from hydrogen and R 2 ; and 
     R 4  and R 5  are independently selected from hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aryl, aralkyl, hydroxyalkyl, alkoxyalkyl, aryloxyalkyl, and acyloxyalkyl, or R 4  and R 5  taken together form a 5- to 7-member heterocyclic ring whose ring atoms are selected from the group consisting of carbon, nitrogen, oxygen and sulfur, wherein the ring atoms include at most 3 heteroatoms. 
     The groups defined as R 2 , R 3 , R 4 , and R 5 , when selected from alkyl, alkenyl, and alkynyl, preferably have up to six carbon atoms. When selected from cycloalkyl or cycloalkenyl, they preferably have 3 to 7, or, for cycloalkenyl, 5 to 7 carbon atoms. When selected from aralkyl, hydroxyalkyl, alkoxyalkyl, aryloxyalkyl, and acyloxyalkyl, the alkyl components of these groups preferably have up to six carbon atoms. In one embodiment, each of these groups is independently selected from alkyl, aryl, aralkyl, and alkoxyalkyl. 
     In selected embodiments, X 2 ═X 3 ═H, and Y is —CH 2 — or —CH 2 CH 2 —. In further embodiments, OR 1  is selected from the group consisting of O—(C═O)—OR 2 , O—(C═O)—O—Y—(C═O)—OR 3 , and O—(C═O)—O—Y—NR 4 R 5 (carbonate derivatives). In other embodiments, OR 1  is-selected from the group consisting of O—(C═O)—NR 4 R 5 , O—(C═O)—NR 3− Y—(C═O)—OR 3 , and O—(C═O)—NR 3 —Y—NR 4 N 5 (carbamate derivatives). 
     These and other objects and features of the invention will become more fully apparent when the following detailed description of the invention is read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a graph showing apoptosis induction by invention compound PG666 (14-ethyl carbamate), in comparison to triptolide (PG490), its 14-succinyl ester (PG490-88), and its 14-glutamyl ester (PG661); see also Table 3. 
         FIG. 2  is a graph showing apoptosis induction by invention compounds PG666 (14-ethyl carbamate), PG671 (14-phenyl carbamate) and PG 672 (N-methylpiperazinecarbonyl) (carbamate), in comparison to triptolide (PG490), its 14-succinyl ester (PG490-88), and its 14-glutamyl ester (PG661); see also Table 4. 
         FIG. 3  is a graph showing apoptosis induction by invention compounds PG666 (14-ethyl carbamate) and PG688 (14-dimethylaminoethyl carbamate), in comparison to triptolide (PG490) and its 14-succinyl ester (PG490-88); see also Table 5. 
         FIG. 4  is a graph showing IL-2 inhibition by invention compounds PG666 (14-ethyl carbamate) and PG688 (14-dimethylaminoethyl carbamate), in comparison to triptolide (PG490) and its 14-succinyl ester (PG490-88); see also Table 7. 
         FIG. 5  is a graph showing IL-2 inhibition by invention compounds PG666 (14-ethyl carbamate), PG671 (14-phenyl carbamate) and PG672 (14-N-methylpiperazinecarbonyl) (carbamate), in comparison to triptolide (PG490), its 14-succinyl ester (PG490-88), and its isoglutamyl ester (PG661); see also Table 8. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     I. Definitions 
     The terms below have the following meanings unless indicated otherwise. 
     “Triptolide derivatives” or “triptolide analogs” refers to derivatives of triptolide, 16-hydroxytriptolide, or tripdiolide (2-hydroxytriptolide) which are derivatized at one or more hydroxyl groups. 
     “Alkyl” refers to a fully saturated acyclic moiety consisting of carbon and hydrogen, which may be linear or branched. Examples of alkyl groups are methyl, ethyl, n-butyl, t-butyl, n-heptyl, and isopropyl. Generally preferred are lower alkyl groups, having one to six carbon atoms, as exemplified by methyl, ethyl, n-butyl, i-butyl, t-butyl, isoamyl, n-pentyl, and isopentyl. 
     “Cycloalkyl” refers to a fully saturated cyclic moiety consisting of carbon and hydrogen, having three to eight carbon atoms, preferably three to six carbons atoms; e.g. cyclopropyl or methylcyclopentyl. “Cycloalkenyl” refers to an unsaturated cyclic moiety consisting of carbon and hydrogen, having five to eight carbon atoms, preferably five or six carbon atoms. 
     “Alkenyl” refers to an unsaturated acyclic moiety consisting of carbon and hydrogen, which may be linear or branched, having one or more double bonds. Generally preferred are lower alkenyl groups, having two to six carbon atoms. “Alkynyl” refers to an unsaturated acyclic moiety consisting of carbon and hydrogen, which may be linear or branched, containing one or more triple bonds. Generally preferred are lower alkynyl groups, having two to six carbon atoms. 
     “Aryl” refers to a substituted or unsubstituted monovalent aromatic radical, generally having a single ring (e.g., benzene) or two condensed rings (e.g., naphthyl), where monocyclic aryl groups are preferred. The term includes heteroaryl groups, which are aromatic ring groups having one or more nitrogen, oxygen, or sulfur atoms in the ring, such as furyl, pyrrole, pyridyl, and indole. By “substituted” is meant that one or more ring hydrogens in the aryl group, preferably one or two ring hydrogens, is replaced with a group preferably selected from fluorine, chlorine, bromine, methyl, ethyl, hydroxy, hydroxymethyl, nitro, amino, methylamino, dimethylamino, methoxy, halomethoxy, and halomethyl. 
     “Acyloxyalkyl” refers to a substituent of the form —R—O—(C═O)—R′, where R is alkyl, preferably having up to six carbon atoms, and R′ is selected from alkyl, alkenyl, alkynyl, aryl, and aralkyl, where R′ preferably comprises lower alkyl, lower alkenyl, or lower alkynyl (i.e. C 2 -C 6 ) groups and monocyclic aryl groups. 
     “Aralkyl” refers to an alkyl, preferably lower (C 1 -C 4 , more preferably C 1 -C 2 ) alkyl, substituent which is further substituted with an aryl group, preferably a monocyclic aryl group; examples are benzyl and phenethyl. Also included is fluorenylmethyl, a component of the widely employed Fmoc (fluorenylmethoxycarbonyl) protecting group. 
     The term “pharmaceutically acceptable salt” encompasses carboxylate salts having organic and inorganic cations, such as alkali and alkaline earth metal cations (for example, lithium, sodium, potassium, magnesium, barium and calcium); ammonium; or organic cations, for example, dibenzylammonium, benzylammonium, 2-hydroxyethylammonium, bis(2-hydroxyethyl)ammonium, phenylethylbenzylammonium, dibenzylethylene diammonium, and the like. Other cations encompassed by the above term include the protonated form of procaine, quinine and N-methylglucosamine, and the protonated forms of basic amino acids such as glycine, ornithine, histidine, phenylglycine, lysine, and arginine. 
     The term also includes salts formed by standard acid-base reactions with basic groups, such as amino groups, having a counterion derived from an organic or inorganic acid. Such counterions include chloride, sulfate, phosphate, acetate, succinate, citrate, lactate, maleate, fumarate, palmitate, cholate, glutamate, glutarate, tartrate, stearate, salicylate, methanesulfonate, benzenesulfonate, sorbate, picrate, benzoate, cinnamate, and the like. 
     For the purposes of the current disclosure, the following numbering scheme is used for triptolide and triptolide analogs: 
     
       
         
         
             
             
         
       
     
     II. Triptolide Analogs 
     Compounds as represented by structure I, below, are derivatives of triptolide having hydrophilic substituents, possess greater water solubility than the non-derivatized starting compound, and are effective to hydrolyze and convert in vivo to the parent compound. The compounds are useful as prodrugs for immunosuppressive, anti-inflammatory and anticancer applications. 
     A. Structure 
     In compounds of formula I: 
     
       
         
         
             
             
         
       
     
     X 1  is OH or OR 1 , and X 2  and X 3  are independently OH, OR 1  or hydrogen, with the proviso that at least one of X 1 , X 2  and X 3  is OR 1 , and at least one of X 2  and X 3  is hydrogen. 
     OR 1  is a carbamate or carbonate group, which may be further substituted, e.g. with an ester or amine. In particular, where OR 1  is represented as O—(C═O)—Z, Z is selected from the group consisting of: 
     —OR 2 , 
     —O—Y—(C═O)—OR 3 , 
     —O—Y—NR 4 R 5 , 
     —NR 4 R 5 , 
     —NR 3 —Y—(C═O)—OR 3 , and 
     —NR 3 —Y—NR 4 N 5 , 
     where Y is a divalent alkyl, alkenyl or alkynyl group having up to six carbon atoms; R 2  is selected from alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aryl, aralkyl, hydroxyalkyl, alkoxyalkyl, aryloxyalkyl, and acyloxyalkyl; and each R 3  is independently selected from hydrogen and R 2 . R 4  and R 5  are independently selected from hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aryl, aralkyl, hydroxyalkyl, alkoxyalkyl, aryloxyalkyl, and acyloxyalkyl. Alternatively, R 4  and R 5  taken together may form a 5- to 7-member heterocyclic ring whose ring atoms are selected from the group consisting of carbon, nitrogen, oxygen and sulfur, where the ring atoms include at most 3 heteroatoms. Examples include, but are not limited to, piperidine, piperazine, pyrrolidine, and morpholine. 
     The groups defined as R 2 , R 3 , R 4 , and R 5 , when selected from alkyl, alkenyl, and alkynyl, preferably have up to six carbon atoms. When selected from cycloalkyl or cycloalkenyl, they preferably have 3 to 7, or, for cycloalkenyl, 5 to 7 carbon atoms. When selected from aralkyl, hydroxyalkyl, alkoxyalkyl, aryloxyalkyl, and acyloxyalkyl, the alkyl components of these groups preferably have up to six carbon atoms. In one embodiment, each of these groups is independently selected from alkyl, aryl, aralkyl, and alkoxyalkyl. 
     In one embodiment, X 1  is OR 1 , and each of X 2  and X 3  is hydrogen. In another embodiment, Y is methylene (—CH 2 —) or ethylene (—CH 2 CH 2 —). 
     B. Preparation 
     The compounds of structure I may be prepared from triptolide, as obtained from the root xylem of the Chinese medicinal plant  Tripterygium wilfordii  (TW) or from other known sources. The TW plant is found in the Fujiang Province and other southern provinces of China; TW plant material can generally be obtained in China or through commercial sources in the United States. Methods for preparing triptolide and some of its derivatives (e.g. tripdiolide and 16-hydroxytriptolide) are known in the art and are described, for example, in Kupchan et al. (1972, 1977); Lipsky et al. (1994); Pu et al. (1990); and Ma et al. (1992). 
     The hydroxyl group(s) of triptolide or its derivatives can be converted to the carbamates of structure I by reaction with an appropriately substituted isocyanate, as shown in Examples 1 (General Procedure A), 5 and 6, or by reaction with phosgene and an appropriately substituted amine, as shown in Examples 2 (General Procedure B) and 7. 
     Similarly, the hydroxyl group(s) of triptolide or its derivatives can be converted to the carbonates of structure I by reaction with an appropriately substituted chloroformate, as shown in Examples 3 (General Procedure C), 8 and 9, or by reaction with phosgene and an appropriately substituted alcohol, as shown in Examples 4 (General Procedure D), 10-13 and 15. As shown in Examples 7 and 11-15, further functionality on a carbonate or carbamate alkyl group can be incorporated. Metal salts and amine salts are readily prepared by reaction or exchange with an appropriate counterion (Examples 14, 16, 17). 
     In cases where all available hydroxyl groups on the starting material are to be derivatized, an excess of reagent can be used to drive the reaction to completion. The compound 16-hydroxytriptolide contains two free hydroxyl groups, one secondary (at C-14) and one primary (at C-16). Since the hydroxyl group at the 16-position is more reactive than the 14-hydroxyl group for steric reasons, mono- and diester derivatives can be selectively made using appropriate reaction conditions. Reaction with a stoichiometric amount of a selected reagent yields primarily the compound monoderivatized at the 16-position, with the 14-hydroxyl group remaining free. Monoderivatives substituted at the more hindered (secondary) hydroxyl group can be prepared by first selectively protecting the less hindered (primary) hydroxyl group, carrying out the derivatization at the unprotected position, and then removing the protecting group. Suitable hydroxyl protecting groups are well known, and are described, for example, by Kocienski (1994). 
     Various compounds of the invention, prepared as described above and in the Examples, are given in the Table below. All are substituted at the 14-hydroxyl of triptolide with a carbonate or carbamate substituent. Also included are reference ester substituted compounds, PC490-88 and PG661, as well as the parent compound, designated herein as PG490. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Exemplary Carbamate- and Carbonate-Substituted Triptolide Derivatives 
               
            
           
           
               
               
               
            
               
                 Designation 
                 Name (Triptolide derivative) 
                 14-O—(C═O)X substituent 
               
               
                   
               
               
                 Controls 
                   
                   
               
               
                 PG490 
                 Triptolide 
                   
               
               
                 PG490-88 
                 14-succinyl ester 
                 CH 2 CH 2 COOH 
               
               
                 PG661 
                 14-isoglutamyl ester 
                 CH 2 CH 2 CH(NH 2 )COOH 
               
               
                 Compounds 
                   
                   
               
               
                 PG666 
                 14-ethyl carbamate 
                 NHCH 2 CH 3   
               
               
                 PG671 
                 14-phenyl carbamate 
                 NH(C 6 H 5 ) 
               
               
                   
               
               
                 PG672 
                 N-methylpiperazinecarbonyl (carbamate) 
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
               
                 PG674 
                 14-ethyl carbonate 
                 OCH 2 CH 3   
               
               
                 PG676 
                 14-phenyl carbonate 
                 O(C 6 H 5 ) 
               
               
                 PG679 
                 14-ethoxyethyl carbonate 
                 OCH 2 CH 2 OCH 2 CH 3   
               
               
                 PG680 
                 14-methoxycarbonylmethyl  
                 OCH 2 (C═O)OCH 3   
               
               
                   
                 carbonate 
                   
               
               
                 PG681 
                 14-(R)-α-methyl-tert- 
                 OC*H(CH 3 )(C═O)OC(CH 3 ) 3   
               
               
                   
                 butoxycarbonylmethyl  
                   
               
               
                   
                 carbonate 
                   
               
               
                 PG682 
                 14-dimethylaminoethyl  
                 OCH 2 CH 2 N(CH 3 ) 2   
               
               
                   
                 carbonate 
                   
               
               
                 PG682 PTSA 
                 14-dimethylaminoethyl  
                 OCH 2 CH 2 N + H(CH 3 ) 2    − OTs 
               
               
                   
                 carbonate, 
                   
               
               
                   
                 p-toluenesulfonate salt 
                   
               
               
                 PG687 
                 14-hydroxycarbonylmethyl  
                 OCH 2 COOH 
               
               
                   
                 carbonate 
                   
               
               
                 PG687 Na 
                 14-hydroxycarbonylmethyl  
                 OCH 2 COO −+ Na 
               
               
                   
                 carbonate, sodium salt 
                   
               
               
                 PG687 tris 
                 14-hydroxycarbonylmethyl  
                 OCH 2 COO −   + NH 3 C(CH 2 OH) 3   
               
               
                   
                 carbonate, tris(hydroxy- 
                   
               
               
                   
                 methyl)aminomethane salt 
                   
               
               
                 PG688 
                 14-dimethylaminoethyl  
                 NHCH 2 CH 2 N(CH 3 ) 2   
               
               
                   
                 carbamate 
                   
               
               
                 PG695 
                 14-tert-butyl carbonate 
                 OC(CH 3 ) 3   
               
               
                   
               
            
           
         
       
     
     III. Prodrug Conversion and Apoptosis Inducing Activity 
     A. Conversion Assays 
     The compounds of formula I provide the advantage of different and sometimes widely varying rates of conversion to parent compound, as demonstrated below. Accordingly, prodrugs of formula I can be selected for different desired conversion rates in human serum/plasma by choosing different structural constituents linked via a carbonate or carbamate linkage to triptolide. 
     Compounds of formula I, as shown in Table 1 above and in the Examples, were assayed for their capacity to induce apoptosis in cells from the Jurkat human T lymphocyte cell line, after incubation with pooled human serum for varying periods of time at 37° C. (see Example 19). An ester prodrug, triptolide-14-succinate, designated PG490-88, was included for comparison. The extent of conversion to triptolide after such incubation was also independently determined by HPLC analysis. 
     The results of the apoptosis assay are presented in Table 2. The ED 50  values (column 3) are calculated directly from the data in each experiment, and the % conversion values (column 4) are calculated as percent of the ED 50  value produced by triptolide, designated PG490, incubated in the same plasma (i.e. in the same experiment). This procedure gives the most valid direct comparison of each compound to triptolide under the same experimental conditions. 
     Comparison of the percent conversion at each of the incubation times shows a broad range of values among the compounds. The percent conversion varied from 7% (PG681; 14-(R)-α-methyl-tert-butoxycarbonylmethyl carbonate) to 98% (PG674; 14-ethyl carbonate) after 1 hour, and from 6% (PG687-tris; 14-hydroxycarbonylmethyl carbonate, tris salt) to 100% (PG674, PG695; 14-tert-butyl carbonate) or greater (PG682; 14-dimethylaminoethyl carbonate, calculated as &gt;100% compared to PG490) after 48 hours. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 ED 50  (nM)  
                 Conversion,  
                   
               
               
                   
                 Incubation 
                 in apoptosis  
                 as relative  
                   
               
               
                   
                 Time in 
                 assay after  
                 ED 50  compared  
                 t 1/2  in human 
               
               
                   
                 Serum 
                 incubation 
                 to triptolide  
                 plasma (min) 
               
               
                 Cmpd. 
                 (hours) 
                 with serum 
                 (%) 
                 by HPLC 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Control 
                   
                   
                   
                   
               
               
                 PG490-88 
                 0.5 
                 2584 
                 2 
                 max. 26% 
               
               
                 PG490-88 
                 1 
                 2268 
                 2 
                 conversion 
               
               
                 PG490-88 
                 24 
                 328 
                 18 
                 at 48 hr  
               
               
                 PG490-88 
                 48 
                 147 
                 43 
                 (Na salt) 
               
               
                 Compounds 
                   
                   
                   
                   
               
               
                 PG674 
                 0.5 
                 27 
                 188 
                 12 
               
               
                 PG674 
                 1 
                 55 
                 98 
                   
               
               
                 PG674 
                 24 
                 60 
                 97 
                   
               
               
                 PG674 
                 48 
                 65 
                 100 
                   
               
               
                 PG676 
                 48 
                 56 
                 96 
                 15 
               
               
                 PG679 
                 0.5 
                 39 
                 128 
                 11 
               
               
                 PG680 
                 48 
                 58 
                 85 
                 9 
               
               
                 PG681 
                 1 
                 684 
                 7 
                 max. 20% 
               
               
                 PG681 
                 48 
                 139 
                 40 
                 conversion at  
               
               
                   
                   
                   
                   
                 48 hr 
               
               
                 PG682 
                 1 
                 66 
                 76 
                 n.d. 
               
               
                 PG682 
                 48 
                 32 
                 146 
                   
               
               
                 PG682PTSA  
                 1 
                 57 
                 89 
                 17 
               
               
                 PG687tris 
                 48 
                 960 
                 6 
                 max. 10% at  
               
               
                   
                   
                   
                   
                 48 hr (Na salt) 
               
               
                 PG695 
                 48 
                 59 
                 100 
                 n.d. 
               
               
                   
               
            
           
         
       
     
     Prodrug conversions to triptolide as determined independently by HPLC are given in column 4. As with the bioassay data, a comparison of the t 1/2  values for conversion to triptolide shows a broad range of values among the compounds. The t 1/2  values range from 9 minutes (PG680; 14-methoxycarbonylmethyl carbonate), 11 minutes (PG679; 14-ethoxyethyl carbonate) and 12 minutes (PG674; 14-ethyl carbonate) to incomplete conversion (10%) in 48 hours of incubation (PG687Na; 14-hydroxycarbonylmethyl carbonate, sodium salt). PG681 (14-(R)-α-methyl-tert-butoxycarbonylmethyl carbonate), which exhibits the lowest percent conversion in the bioassay (7%), converts incompletely (20%) in 48 hours as assessed by HPLC. PG687 (14-hydroxycarbonylmethyl carbonate) converts only 6% within 48 hours when evaluated in the apoptosis assay, and only 10% in this time span when assayed by HPLC. PG674 (14-ethyl carbonate) converts 98% in 1 hour and 100% in 48 hours in the bioassay, and exhibits a t 1/2  of 12 minutes by HPLC analysis. PG682 (14-dimethylaminoethyl carbonate) displays conversion calculated as &gt;100% in is apoptosis induction, and a 17 minute t 1/2  by HPLC evaluation. 
     There is a large measure of consistency between the results of prodrug conversion in human serum to a biologically active, apoptosis-inducing compound (presumably triptolide) and the conversion in human plasma and expressed in minutes as the t 1/2  of prodrug conversion to triptolide assessed by HPLC. There is a broad range of values for the conversion of prodrugs, whether the conversion is evaluated in the apoptosis induction bioassay or by HPLC identification and quantification of triptolide. This broad range of conversion values in human serum or plasma indicates that the compounds of formula I do not share a similar conversion rate under these circumstances. This unexpected difference in conversion rates from these triptolide prodrugs to triptolide shows that different and widely varying rates of conversion can be obtained by making differently substituted prodrugs as described herein. 
     In general, the carbamate derivatives of the invention, as a class, were found to convert in human serum less readily than the carbonate derivatives, as a class. As discussed further below, derivatives which are resistant to hydrolysis by human esterases and proteases may be useful in antibody directed enzyme prodrug therapy. 
     B. Dose-Response Data 
     Dose-response data on apoptosis induction by invention compound PG666 (14-ethyl carbamate), in comparison to triptolide (PG490), its 14-succinyl ester (PG490-88), and its 14-glutamyl ester (PG661), is given in Table 3. The dose-response data is also represented graphically in  FIG. 1 . 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Apoptotic Induction by Triptolide Esters and Carbamate PG666 in the Presence 
               
               
                 of Human Serum 
               
            
           
           
               
               
            
               
                   
                 % apoptotic cells at given concentration (nM) 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 1 
                 3 
                 10 
                 30 
                 100 
                 300 
                 1000 
                 3000 
                 10000 
               
               
                   
               
            
           
           
               
               
            
               
                 Human serum, 48 hr 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 PG490 (cntrl) 
                  8.5 
                  8.5 
                  8.5 
                 26.2 
                 91.7 
                 93.4 
                 94.6 
                 95.2 
                 95.4 
               
               
                 PG490-88 (cntrl) 
                  7.8 
                  8.1 
                  7.8 
                  9.1 
                 51.5 
                 92.1 
                 93.9 
                 94.1 
                 95.1 
               
               
                 PG661 (cntrl) 
                 11.3 
                 10.4 
                 10.3 
                 10.5 
                 10.3 
                 10.5 
                 10.2 
                  9.7 
                  9.4 
               
               
                 PG666 
                 13.4 
                 14.4 
                 14.0 
                 10.1 
                 11.0 
                 20.6 
                 91.0 
                 92.9 
                 93.5 
               
            
           
           
               
               
            
               
                 Human serum, 0 hr 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 PG490 (cntrl) 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 94.9 
               
               
                 PG490-88 (cntrl) 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 89.2 
               
               
                 PG661 (cntrl) 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                  7.9 
               
               
                 PG666 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 93.6 
               
            
           
           
               
               
            
               
                 Medium only 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 PG490 (cntrl) 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 96.5 
               
               
                 PG490-88 (cntrl) 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 93.8 
               
               
                 PG661 (cntrl) 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 13.6 
               
               
                 PG666 + medium 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 94.3 
               
            
           
           
               
               
            
               
                 Other controls 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 DMSO + Hu 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                  7.5 
               
               
                 PBS + Hu 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                  7.5 
               
               
                 Medium 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                  7.8 
               
               
                   
               
            
           
         
       
     
     Dose-response data on apoptosis induction by invention compounds PG666 (14-ethyl carbamate), PG671 (14-phenyl carbamate) and PG 672 (N-methylpiperazinecarbonyl) (carbamate), in comparison to triptolide (PG490), its 14-succinyl ester (PG490-88), and its 14-glutamyl ester (PG661), is given in Table 4. The dose-response data is also represented graphically in  FIG. 2 . (Some assays gave a higher apparent background apoptosis than is usually seen, which is assumed to be an artifact isolated to this experiment.) 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Apoptotic Induction by Triptolide Esters and Carbamates in the Presence of  
               
               
                 Human Serum 
               
            
           
           
               
               
            
               
                   
                 % apoptotic cells at given concentration (nM) 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 0.03 
                 0.1 
                 0.3 
                 1 
                 3 
                 10 
                 30 
                 100 
                 300 
                 1000 
                 3000 
                 10000 
               
               
                   
               
            
           
           
               
               
            
               
                 Serum, 48 hr 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 PG666 
                 39.9 
                 40.7 
                 40.8 
                 41.3 
                 39.8 
                 39.8 
                 39.1 
                 40.2 
                 44.5 
                 88.6 
                 96.8 
                 92.3 
               
               
                 PG671 
                 42.5 
                 43.3 
                 43.9 
                 44.2 
                 43.2 
                 42.4 
                 44.7 
                 43.5 
                 43.1 
                 43.0 
                 43.3 
                 15.4 
               
               
                 PG672 
                 42.7 
                 45.2 
                 45.4 
                 45.9 
                 45.3 
                 46.0 
                 46.8 
                 46.6 
                 42.3 
                 43.7 
                 44.9 
                 63.2 
               
            
           
           
               
               
            
               
                 Controls 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 PG490 
                  7.0 
                  6.9 
                  6.8 
                  6.4 
                  7.0 
                  7.1 
                 29.4 
                 90.9 
                 93.0 
                 93.2 
                 94.6 
                 94.2 
               
               
                 PG490-88 
                  6.6 
                  6.5 
                  7.0 
                  6.0 
                  6.2 
                  6.2 
                  6.8 
                 30.5 
                 89.6 
                 92.6 
                 92.8 
                 93.9 
               
               
                 PG661 
                 38.8 
                 38.2 
                 39.0 
                 39.2 
                 39.1 
                 39.2 
                 40.3 
                 38.6 
                 36.3 
                 28.7 
                 28.2 
                  5.2 
               
            
           
           
               
               
            
               
                 Serum, 0 hr 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 PG666 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 87.2 
               
               
                 PG671 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 10.2 
               
               
                 PG672 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 47.6 
               
            
           
           
               
               
            
               
                 Controls 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 PG490 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 92.1 
               
               
                 PG490-88 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 82.9 
               
               
                 PG661 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                  5.2 
               
            
           
           
               
               
            
               
                 Medium 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 PG666 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 92.6 
               
               
                 PG671 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 13.7 
               
               
                 PG672 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 48.6 
               
            
           
           
               
               
            
               
                 Controls 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 PG490 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 93.4 
               
               
                 PG490-88 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 89.7 
               
               
                 PG661 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                  7.3 
               
               
                 DMSO + Hu 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                  6.7 
               
               
                 PBS + Hu 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                  6.6 
               
               
                   
               
            
           
         
       
     
     Dose-response data on apoptosis induction by invention compounds PG666 (14-ethyl carbamate) and PG688 (14-dimethylaminoethyl carbamate), in comparison to triptolide (PG490) and its 14-succinyl ester (PG490-88), is given in Table 5. The dose-response data is also represented graphically in  FIG. 3 . 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Apoptotic Induction by Triptolide Esters and Carbamates 
               
               
                 in the Presence of Human Serum (48 hrs) 
               
            
           
           
               
               
            
               
                   
                 % apoptotic cells at given concentration (nM) 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 1 
                 3 
                 10 
                 30 
                 100 
                 300 
                 1000 
                 3000 
               
               
                   
               
               
                 Human serum 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 PG490 (cntrl) 
                  8.8 
                  8.5 
                  8.6 
                 15.9 
                 86.5 
                 90.7 
                 91.7 
                 93.1 
               
               
                 PG490-88  
                  8.6 
                  9.3 
                  8.7 
                  7.8 
                 23.3 
                 88.4 
                 90.5 
                 91.7 
               
               
                 (cntrl) 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 PG688 
                  9.2 
                  9.8 
                  9.4 
                  9.5 
                  9.4 
                  8.7 
                  8.6 
                  8.2 
               
               
                 PG666 
                  9.8 
                 10.9 
                 10.4 
                 10.2 
                  9.5 
                 14.9 
                 87.7 
                 91.0 
               
               
                 Medium 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 PG490 (cntrl) 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 93.7 
               
               
                 PG490-88  
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 64.8 
               
               
                 (cntrl) 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 PG688 
                 13.0 
                 14.0 
                 12.1 
                 10.9 
                 11.2 
                 11.3 
                 12.1 
                 10.9 
               
               
                 PG666 
                 13.9 
                 13.1 
                 13.4 
                 13.0 
                 13.2 
                 14.2 
                 14.1 
                 92.1 
               
               
                 Other controls 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Medium 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                  9.1 
               
               
                 DMSO + Hu 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                  9.2 
               
               
                 PBS + Hu 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                  9.1 
               
               
                   
               
            
           
         
       
     
     Inspection of the dose-response data for these compounds shows PG666 (14-ethyl carbamate) to be more active than PG688 (4-dimethylaminoethyl carbamate) and PG671 (14-phenyl carbamate) after 48 hr. incubation in human serum. PG666 showed equal apoptotic activity to PG490 (triptolide) at roughly a 10-fold higher concentration. The N-methylpiperazinecarbamate (PG672) showed activity at high concentrations ( FIG. 2 ), while to the isoglutamyl ester (PG661) showed essentially no activity ( FIGS. 1-2 ). 
     III. Anticancer Treatment 
     Triptolide prodrugs have shown effectiveness in cancer treatment in vivo. See, for example, coowned PCT Publication No. WO 02/56835, which is incorporated herein by reference. This document describes high efficacy of a triptolide prodrug, in comparison to 5-FU and CPT-11, in studies with tumor xenografts of the LIT-29 human colon cancer cell line. The triptolide prodrug (a 14-succinate derivative of triptolide) strongly inhibited tumor growth, to a significantly greater degree than 5-FU and CPT-11, and induced tumor regression. 
     The invention thus includes the use of a composition as described herein to treat cancers, including cancers involving cells derived from reproductive tissue (such as Sertoli cells, germ cells, developing or more mature spermatogonia, spermatids or spermatocytes and nurse cells, germ cells and other cells of the ovary), the lymphoid or immune systems (such as Hodgkin&#39;s disease and non-Hodgkin&#39;s lymphomas), the hematopoietic system, and epithelium (such as skin and gastrointestinal tract), solid organs, the nervous system, and musculo-skeletal tissue. The triptolide prodrugs may be used for treatment of various cancer cell types, including, but not limited to, breast, colon, small cell lung, large cell lung, prostate, malignant melanoma, liver, kidney, pancreatic, esophogeal, stomach, ovarian, cervical or lymphoma tumors. Treatment of breast, colon, lung, and prostate tumors is particularly contemplated. Treatment of leukemias is also contemplated. The composition may be administered to a patient afflicted with cancer and/or leukemia by any conventional route of administration, as discussed above. 
     The method is useful to slow the growth of tumors, prevent tumor growth, induce partial regression of tumors, and induce complete regression of tumors, to the point of complete disappearance. The method is also useful in preventing the outgrowth of metastases derived from solid tumors. 
     The compositions of formula I may be administered as sole therapy or with other supportive or therapeutic treatments not designed to have anti-cancer effects in the subject. The method also includes administering the compounds of formula I in combination with one or more conventional anti-cancer drugs or biologic protein agents, where the amount of drug(s) or agent(s) is, by itself, ineffective to induce the appropriate suppression of cancer growth, in an amount effective to have the desired anti-cancer effects in the subject. Such anti-cancer drugs include actinomycin D, camptothecin, carboplatin, cisplatin, cyclophosphamide, cytosine arabinoside, daunorubicin, doxorubicin, etoposide, fludarabine, 5-fluorouracil, hydroxyurea, gemcitabine, irinotecan, methotrexate, mitomycin C, mitoxantrone, paclitaxel, taxotere, teniposide, topotecan, vinblastine, vincristine, vindesine, and vinorelbine. Anti-cancer biologic protein agents include tumor necrosis factor (TNF), TNF-related apoptosis inducing ligand (TRAIL), other TNF-related or TRAIL-related ligands and factors, interferon, interleukin-2, other interleukins, other cytokines, chemokines, and factors, antibodies to tumor-related molecules or receptors (such as anti-HER2 antibody), and agents that react with or bind to these agents (such as members of the TNF super family of receptors, other receptors, receptor antagonists, and antibodies with specificity for these agents). 
     IV. Prodrug Conversion and Cytokine Inhibiting Activity 
     A. Conversion Assays 
     As discussed above, the compounds of formula I provide the advantage of different and sometimes widely varying rates of conversion to parent compound. Accordingly, prodrugs of formula I can be selected for different conversion rates in human serum/plasma by choosing different structural constituents linked via a carbonate or carbamate linkage to triptolide. 
     Several compounds of formula I were analyzed for their capacity to inhibit IL-2 production in Jurkat human T lymphocyte cells, after incubation with pooled human serum for 48 hours at 37° C. (see Example 20). An ester prodrug, triptolide-14-succinate, designated PG490-88, was included for comparison. 
     The results of the immunosuppression assay are presented in Table 6. The IC 50  values (column 1) are calculated directly from the data in each experiment. The % conversion values (column 2) are calculated as the percent of the IC 50  value produced by triptolide, designated PG490, incubated in the same plasma (i.e. in the same experiment). 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                 Compound 
                 IC 50  (nM) 
                 Conversion (%) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 PG490-88 (cntrl) 
                 9 
                 51 
               
               
                   
                 PG682PTSA 
                 2 
                 97 
               
               
                   
                 PG680 
                 3 
                 44 
               
               
                   
                 PG681 
                 3 
                 55 
               
               
                   
                 PG676 
                 6 
                 84 
               
               
                   
                 PG679 
                 12 
                 11 
               
               
                   
                 PG682 
                 23 
                 78 
               
               
                   
                 PG687tris 
                 29 
                 6 
               
               
                   
                 PG687 
                 61 
                 2 
               
               
                   
                 PG687Na 
                 92 
                 1 
               
               
                   
                 PG695 
                 100 
                 2 
               
               
                   
                   
               
            
           
         
       
     
     Again, a broad range of values is shown for the conversion of the prodrugs as evaluated in the IL-2 inhibition assay. This broad range of conversion values in human serum or plasma indicates that the compounds of formula I do not share a similar conversion rate under these circumstances. This unexpected difference in conversion rates from these triptolide prodrugs to triptolide shows that different and widely varying rates of conversion can be obtained by making differently substituted prodrugs as described herein. 
     B. Dose-Response Data 
     Dose-response data on IL-2 inhibition by invention compounds PG666 (14-ethyl carbamate) and PG688 (14-dimethylaminoethyl carbamate), in comparison to triptolide (PG490) and its 14-succinyl ester (PG490-88), is given in Table 7. The dose-response data is also represented graphically in  FIG. 4 . 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Inhibition of IL-2 production in Jurkat cells (48 hrs) 
               
            
           
           
               
               
            
               
                   
                 IL-2 pg/mL at given concentration (nM) 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 0 
                 0.001 
                 0.01 
                 0.1 
                 1 
                 10 
                 100 
                 1000 
                 10000 
               
               
                   
               
               
                 Controls 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 PG490 
                 932.4 
                 929.7 
                 908.6 
                 937.8 
                 835.2 
                 556.1 
                 120.7 
                  62.9 
                  59.2 
               
               
                 PG490- 
                 838.0 
                 776.4 
                 771.0 
                 809.5 
                 732.4 
                 605.1 
                 317.5 
                  65.9 
                  58.2 
               
               
                 88 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Com- 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 pounds 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 PG688,  
                 848.5 
                 883.9 
                 754.1 
                 810.4 
                 900.4 
                 796.3 
                 873.3 
                 759.9 
                 459.8 
               
               
                 serum 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 PG666,  
                 846.0 
                 844.6 
                 799.8 
                 860.6 
                 773.0 
                 819.1 
                 528.0 
                 180.1 
                  63.5 
               
               
                 serum 
               
               
                   
               
            
           
         
       
     
     Dose-response data on IL-2 inhibition by invention compounds PG666 (14-ethyl carbamate), PG671 (14-phenyl carbamate) and PG672 (14-N-methylpiperazinecarbonyl) (carbamate), in comparison to triptolide (PG490), its 14-succinyl ester (PG490-88), and its isoglutamyl ester (PG661), is given in Table 8. The dose-response data is also represented graphically in  FIG. 5 . 
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 Inhibition of IL-2 production in Jurkat cells 
               
            
           
           
               
               
            
               
                   
                 IL-2 pg/mL at given concentration (nM) 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 0 
                 0.0001 
                 0.001 
                 0.01 
                 0.1 
                 1 
                 10 
                 100 
                 1000 
                 10000 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Compounds 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 PG666 
                 104.5 
                 94.3 
                 105.1 
                 97.0 
                 92.8 
                 80.0 
                 89.8 
                 33.3 
                 10.0 
                 8.0 
               
               
                 PG671 
                 117.7 
                 96.4 
                 102.7 
                 99.7 
                 114.7 
                 106.1 
                 90.7 
                 77.9 
                 48.7 
                 8.8 
               
               
                 PG672 
                 92.0 
                 103.3 
                 90.8 
                 99.1 
                 117.1 
                 91.4 
                 99.1 
                 64.6 
                 26.8 
                 8.7 
               
               
                 Controls 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 PG490 
                 77.4 
                 80.0 
                 97.2 
                 83.2 
                 87.1 
                 75.7 
                 25.5 
                 17.8 
                 12.9 
                 22.3 
               
               
                 PG490-88 
                 79.0 
                 96.1 
                 83.0 
                 87.5 
                 86.3 
                 88.2 
                 42.7 
                 14.0 
                 8.4 
                 23.8 
               
               
                 PG661 
                 94.9 
                 82.0 
                 102.1 
                 123.6 
                 120.7 
                 98.2 
                 110.3 
                 103.6 
                 74.4 
                 68.7 
               
               
                   
               
            
           
         
       
     
     Several of the invention compounds (PG666, 14-ethyl carbamate; PG688, 4-dimethylaminoethyl carbamate; PG671, 14-phenyl carbamate; and PG672, N-methylpiperazinecarbamate) showed some level of bioactivity in these assays ( FIGS. 4-5 ). Again, the isoglutamyl ester (PG661) showed little or no activity ( FIG. 5 ). PG666 (14-ethyl carbamate) showed equal IL-2 inhibitory activity to PG490 (triptolide) at about 10-30 times the active concentration of PG490. 
     V. Immunomodulating and Antiinflammatory Treatment 
     Pharmaceutical compositions comprising compounds of formula I, which are prodrugs of triptolide, are useful in other applications for which triptolide has proven effective, e.g. in immunosuppression therapy, as in treating an autoimmune disease, preventing transplantation rejection, or treating or preventing graft-versus-host disease (GVHD). 
     The method is useful for inhibiting rejection of a solid organ transplant, tissue graft, or cellular transplant from an incompatible human donor, thus prolonging survival and function of the transplant, and survival of the recipient. This use would include, but not be limited to, solid organ transplants (such as heart, kidney and liver), tissue grafts (such as skin, intestine, pancreas, gonad, bone, and cartilage), and cellular transplants (such as cells from pancreas, brain and nervous tissue, muscle, skin, bone, cartilage and liver). 
     The method is also useful for inhibiting xenograft (interspecies) rejection; i.e. in preventing the rejection of a solid organ transplant, tissue graft, or cellular transplant from a non-human animal, whether natural in constitution or bioengineered (genetically manipulated) to express human genes, RNA, proteins, peptides or other non-native, xenogeneic molecules, or bioengineered to lack expression of the animal&#39;s natural genes, RNA, proteins, peptides or other normally expressed molecules. The invention also includes the use of a composition as described above to prolong the survival of such a solid organ transplant, tissue graft, or cellular transplant from a non-human animal. 
     In another aspect, the invention includes a method of treatment or prevention of graft-versus-host disease, resulting from transplantation into a recipient of matched or mismatched bone marrow, spleen cells, fetal tissue, cord blood, or mobilized or otherwise harvested stem cells. The dose is preferably in the range 0.25-2 mg/kg body weight/day, preferably 0.5-1 mg/kg/day, given orally or parenterally. 
     Also included are methods of treatment of autoimmune diseases or diseases having autoimmune manifestations, such as Addison&#39;s disease, autoimmune hemolytic anemia, autoimmune thyroiditis, Crohn&#39;s disease, diabetes (Type I), Graves&#39; disease, Guillain-Barre syndrome, systemic lupus erythematosus (SLE), lupus nephritis, multiple sclerosis, myasthenia gravis, psoriasis, primary biliary cirrhosis, rheumatoid arthritis and uveitis, asthma, atherosclerosis, Type I diabetes, psoriasis, and various allergies. In treating an autoimmune condition, the patient is given the composition on a periodic basis, e.g., 1-2 times per week, at a dosage level sufficient to reduce symptoms and improve patient comfort. For treating rheumatoid arthritis, in particular, the composition may be administered by intravenous injection or by direct injection into the affected joint. The patient may be treated at repeated intervals of at least 24 hours, over a several week period following the onset of symptoms of the disease in the patient. 
     Immunosuppressive activity of compounds in vivo can be evaluated by the use of established animal models known in the art. Such assays may be used to evaluate the relative effectiveness of immunosuppressive compounds and to estimate appropriate dosages for immunosuppressive treatment. These assays include, for example, a well-characterized rat model system for allografts, described by Ono and Lindsey (1969), in which a transplanted heart is attached to the abdominal great vessels of an allogeneic recipient animal, and the viability of the transplanted heart is gauged by the heart&#39;s ability to beat in the recipient animal. A xenograft model, in which the recipient animals are of a different species, is described by Wang (1991) and Murase (1993). A model for evaluating effectiveness against GVHD involves injection of normal F 1  mice with parental spleen cells; the mice develop a GVHD syndrome characterized by splenomegaly and immunosuppression (Korngold, 1978; Gleichmann, 1984). Single cell suspensions are prepared from individual spleens, and microwell cultures are established in the presence and absence of concanavalin A to assess the extent of mitogenic responsiveness. 
     For therapy in transplantation rejection, the method is intended particularly for the treatment of rejection of heart, kidney, liver, cellular, and bone marrow transplants, and may also be used in the treatment of GVHD. The treatment is typically initiated perioperatively, either soon before or soon after the surgical transplantation procedure, and is continued on a daily dosing regimen, for a period of at least several weeks, for treatment of acute transplantation rejection. During the treatment period, the patient may be tested periodically for immunosuppression level, e.g., by a mixed lymphocyte reaction involving allogenic lymphocytes, or by taking a biopsy of the transplanted tissue. 
     In addition, the composition may be administered chronically to prevent graft rejection, or in treating acute episodes of late graft rejection. As above, the dose administered is preferably 1-25 mg/kg patient body weight per day, with lower amounts being preferred for parenteral administration, and higher amounts for oral administration. The dose may be increased or decreased appropriately, depending on the response of the patient, and over the period of treatment, the ability of the patient to resist infection. 
     The compounds are also useful as potentiators when administered concurrently with another immunosuppressive drug for immunosuppressive treatments as discussed above. A conventional immunosuppressant drug, such as cyclosporin A, FK506, azathioprine, rapamycin, mycophenolic acid, or a glucocorticoid, may thus be administered in an amount substantially less (e.g. 20% to 50% of the standard dose) than when the compound is administered alone. Alternatively, the triptolide analog and immunosuppressive drug are administered in amounts such that the resultant immunosuppression is greater than what would be expected or obtained from the sum of the effects obtained with the drug and triptolide analog used alone. Typically, the immunosuppressive drug and potentiator are administered at regular intervals over a time period of at least 2 weeks. 
     The compositions of formula I are also useful for the treatment of inflammatory conditions such as asthma, both intrinsic and extrinsic manifestations. For treatment of asthma, the composition is preferably administered via inhalation, but any conventional route of administration may be useful. The composition and method may also be used for treatment of other inflammatory conditions, including traumatic inflammation, inflammation in Lyme disease, psoriasis, chronic bronchitis (chronic infective lung disease), chronic sinusitis, sepsis associated acute respiratory distress syndrome, Behcet&#39;s disease, pulmonary sarcoidosis, pemphigus, pemphigoid inflammatory bowel disease, and ulcerative colitis. Triptolide and the present analogs are also useful in reducing male fertility. 
     The compositions of formula I may also be administered in combination with a conventional anti-inflammatory drug (or drugs), where the drug or amount of drug administered is, by itself, ineffective to induce the appropriate suppression or inhibition of inflammation. 
     The dose that is administered is preferably in the range of 1-25 mg/kg patient body weight per day, with lower amounts being preferred for parenteral administration, and higher amounts being preferred for oral administration. Optimum dosages can be determined by routine experimentation according to methods known in the art. 
     VI. Prodrugs of Triptolide as Substrates for Antibody-Conjugated Enzymes 
     Triptolide derivatives which are resistant to hydrolysis by human esterases and proteases may be advantageously employed in antibody directed enzyme prodrug therapy. In this methodology, an anti-tumor antibody is conjugated to an appropriate enzyme (e.g., carboxypeptidase G2) and allowed to localize to a tumor, while clearing from normal tissues. A non-toxic prodrug is then delivered, and is activated to a toxic drug specifically by enzyme at the tumor site. (See e.g. Bagshawe 1987, 1989, 1993; Bagshawe et al. 1988). 
     An enzyme that hydrolyzes an oxygen-carbonyl-nitrogen moiety may be used to convert the less readily converted carbamates of the invention (e.g. PG671, PG672, PG688). Antibody-conjugated enzymes capable of hydrolyzing a carbamate ester bond are known; see e.g. Wentworth et al. 1996. Accordingly, the above carbamates of triptolide may be useful as prodrugs that are significantly less toxic and would be liberated at a tumor site in to the presence of antibody-conjugated enzymes. 
     VII. Therapeutic Compositions 
     Formulations containing the triptolide analogs of formula I may take the form of solid, semi-solid, lyophilized powder, or liquid dosage forms, such as tablets, capsules, powders, sustained-release formulations, solutions, suspensions, emulsions, ointments, lotions, or aerosols, preferably in unit dosage forms suitable for simple administration of precise dosages. The compositions typically include a conventional pharmaceutical carrier or excipient and may additionally include other medicinal agents, carriers, or adjuvants. Preferably, the composition will be about 0.5% to 75% by weight of a compound or compounds of formula I, with the remainder consisting of suitable pharmaceutical excipients. For oral administration, such excipients include pharmaceutical grades of mannitol, lactose, starch, magnesium stearate, sodium saccharine, talcum, cellulose, glucose, gelatin, sucrose, magnesium carbonate, and the like. If desired, the composition may also contain minor amounts of non-toxic auxiliary substances such as wetting agents, emulsifying agents, or buffers. 
     The composition may be administered to a subject orally, transdermally or parenterally, e.g., by intravenous, subcutaneous, intraperitoneal, or intramuscular injection. For use in oral liquid preparation, the composition may be prepared as a solution, suspension, emulsion, or syrup, being supplied either in liquid form or a dried form suitable for hydration in water or normal saline. For parenteral administration, an injectable composition for parenteral administration will typically contain the triptolide analog in a suitable intravenous solution, such as sterile physiological salt solution. 
     Liquid compositions can be prepared by dissolving or dispersing the triptolide analog (about 0.5% to about 20%) and optional pharmaceutical adjuvants in a carrier, such as, for example, aqueous saline, aqueous dextrose, glycerol, or ethanol, to form a solution or suspension. The high water solubility of the compounds of formula I make them particularly advantageous for administering in aqueous solution, e.g. by intraperitoneal injection. Although aqueous solutions are preferred, compositions in accordance with formula I may also be formulated as a suspension in a lipid (e.g., a triglyceride, a phospholipid, or a polyethoxylated castor oil such as “CREMOPHOR EL™”), in a liposomal suspension, or in an aqueous emulsion. 
     The compound may also be administered by inhalation, in the form of aerosol particles, either solid or liquid, preferably of respirable size. Such particles are sufficiently small to pass through the mouth and larynx upon inhalation and into the bronchi and alveoli of the lungs. In general, particles ranging from about 1 to 10 microns in size, and preferably less than about 5 microns in size, are respirable. Liquid compositions for inhalation comprise the active agent dispersed in an aqueous carrier, such as sterile pyrogen free saline solution or sterile pyrogen free water. If desired, the composition may be mixed with a propellant to assist in spraying the composition and forming an aerosol. 
     Methods for preparing such dosage forms are known or will be apparent to those skilled in the art; for example, see  Remington&#39;s Pharmaceutical Sciences  (19th Ed., Williams &amp; Wilkins, 1995). The composition to be administered will contain a quantity of the selected compound in a pharmaceutically effective amount for effecting immunosuppression in a subject. 
     EXAMPLES 
     The following examples illustrate but are not intended in any way to limit the invention. 
     Example 1 
     Preparation of a Triptolide Carbamate by Reaction with an Isocyanate (General Procedure A) 
     
       
         
         
             
             
         
       
     
     A mixture of triptolide, 1 (0.20 mmol, 1.0 eq) and an isocyanate (3.0 mmol, 15.0 eq) in N,N-dimethylformamide (DMF, 7.0 ml) is sealed and heated in 54° C. oil bath with stirring. The reaction is monitored with TLC. After the starting material is completely consumed, the reaction mixture is concentrated under vacuum, and the crude product is purified with preparative TLC. 
     Example 2 
     Preparation of a Triptolide Carbamate by Reaction with Phosgene and an Amine (General Procedure B) 
     
       
         
         
             
             
         
       
     
     To a solution of triptolide, 1 (0.325 mmol, 1.0 eq) and 4-dimethylaminopyridine (DMAP, 0.0377 mmol, 0.12 eq) in 1,4-dioxane (15 ml) is added with stirring pyridine (1.0 ml) and phosgene (˜20% in toluene, 1.19 ml, 2.25 mmol, 6.92 eq) at room temperature under nitrogen. After 1 hour of stirring at room temperature, the reaction mixture is concentrated under vacuum. To the residue is added dichloromethane (DCM, 15.0 ml) and then the amine (R 6 R 7 NH, 1.0 ml). After 10 minutes of stirring at room temperature, the reaction mixture is concentrated under vacuum, and the crude product is purified with preparative TLC. 
     Example 3 
     Preparation of a Triptolide Carbonate by Reaction with a Chloroformate (General Procedure C) 
     
       
         
         
             
             
         
       
     
     To a solution of triptolide, 1 (0.33 mmol, 1.0 eq) and 4-dimethylaminopyridine (DMAP, 3.92 mmol, 11.9 eq) in dichloromethane (DCM, 15 ml) is added with stirring a chloroformate (2.15 mmol, 6.5 eq) at room temperature under nitrogen. After 24 hours of stirring at room temperature, the reaction mixture is concentrated under vacuum, and the crude product is purified with preparative TLC. 
     Example 4 
     Preparation of a Triptolide Carbonate by Reaction with Phosgene and an Alcohol (General Procedure D) 
     
       
         
         
             
             
         
       
     
     To a solution of triptolide, 1 (0.30 mmol, 1.0 eq) and 4-dimethylaminopyridine (DMAP, 3.60 mmol, 12.0 eq) in 1,4-dioxane (15 ml) is added with stirring phosgene (−20% in toluene, 0.79 ml, 1.50 mmol, 5.0 eq) at room temperature under nitrogen. After 1 hour of stirring at room temperature, the reaction mixture is concentrated under vacuum. To the residue is added dichloromethane (DCM, 15 ml) and then the alcohol (R 2 OH, 1.0 ml). After stirring at room temperature overnight, the reaction mixture is concentrated under vacuum, and the crude product is purified with preparative TLC. 
     Example 5 
     Synthesis of Triptolide 14-Ethyl Carbamate (PG666) 
     
       
         
         
             
             
         
       
     
     Using General Procedure A, the product was obtained in 98.5% yield from ethyl isocyanate and triptolide. Analytical TLC Rf=0.44 (ethyl acetate/hexanes/methanol 1:1:0.1). IR (KBr): 3369.6, 2975.6, 2937.6, 2878.0, 1753.0, 1719.0, 1686.1, 1676.5, 1524.0, 1517.7, 1509.0, 1458.7, 1448.8, 1245.8, 1142.5, 1076.3, 1030.8, 988.1, 944.4, 866.9, 722.6, 560.5 cm −1 . H 1  NMR (300 MHz, CDCl 3 ): δ=4.94 (1H, s, 14-CH), 4.68 (2H, s, 19-CH 2 ), 3.83 (1H, d, 11-CH), 3.51 (1H, d, 12-CH), 3.48 (1H, d, 7-CH), 3.26 {2H, m, 22-CH 2  (—N CH 2   CH 3 )}, 2.70 (1H, m, 5-CH), 2.32 (1H, m, 2-CHb), 2.13 (2H, m, 6-CHb and 2-CHa), 1.93 (2H, m, 15-CH and 6-CHa), 1.57 (1H, dd, 1-CHb), 1.22 (1H, m, 1-CHa), 1.16 {3H, t, 23-CH 3  (—NCH 2   CH 3   )}, 1.07 (3H, s, 20-CH 3 ), 0.99 (3H, d, 17-CH 3 ), 0.86 (3H, d, 16-CH 3 ) ppm. HRMS (FAB) m/z calcd for C 23 H 30 NO 7   +  (MH + ) 432.2022. found 432.2016. 
     Example 6 
     Synthesis of Triptolide 14-Phenyl Carbamate (PG671) 
     
       
         
         
             
             
         
       
     
     Using General Procedure A, the product was obtained in 87.0% yield from phenyl isocyanate and triptolide. Analytical TLC Rf=0.51 (ethyl acetate/hexanes/methanol 1:1:0.1). IR (KBr): 3315.3, 2970.4, 2939.5, 2878.3, 1751.9, 1676.6, 1600.8, 1543.0, 1534.7, 1443.6, 1314.6, 1215.3, 1063.3, 1028.5, 761.0, 693.1 cm −1 . H 1  NMR (300 MHz, CDCl 3 ): δ=7.43 (2H, d, Ar—H), 7.30 (2H, dd, Ar—H), 7.07 (1H, t, Ar—H), 5.04 (1H, s, 14-CH), 4.82 (2H, s, 19-CH 2 ), 3.88 (1H, d, 11-CH), 3.57 (1H, d, 12-CH), 3.52 (1H, d, 7-CH), 2.67 (1H, m, 5-CH), 2.33 (1H, d, 2-CHb), 2.17 (2H, m, 6-CHb and 2-CHa), 1.96 (2H, m, 15-CH and 6-CHa), 1.58 (1H, dd, 1-CHb), 1.25 (1H, m, 1-CHa), 1.08 (3H, s, 20-CH 3 ), 1.02 (3H, d, 17-CH 3 ), 0.88 (3H, d, 16-CH 3 ) ppm. 
     Example 7 
     Synthesis of Triptolide 14-Dimethylaminoethyl Carbamate (PG688) 
     
       
         
         
             
             
         
       
     
     Using General Procedure B, the product was obtained in 79.9% yield from triptolide, phosgene and N,N-dimethylethylenediamine. Analytical TLC Rf=0.45 (ethyl acetate/hexanes/methanol/triethylamine 1.2:0.8:0.2:0.1). IR (KBr): 3380.1, 2969.6, 2827.3, 2780.3, 1753.4, 1720.3, 1675.8, 1560.7, 1542.0, 1523.8, 1459.4, 1448.6, 1388.3, 1348.3, 1254.3, 1132.9, 1069.9, 1023.7, 888.2, 773.7, 561.0, 522.3 cm −1 . H 1  NMR (300 MHz, CDCl 3 ): δ=5.57 (1H, t, CONH—), 4.94 (1H, s, 14-CH), 4.68 (2H, s, 19-CH 2 ), 3.83 (1H, d, 11-CH), 3.52 (1H, d, 12-CH), 3.48 (1H, d, 7-CH), 3.31 {2H, m, 22-CH 2 (CONH CH 2   CH 2 )}, 2.69 (1H, m, 5-CH), 2.48 {2H, dd, 23-CH 2  (CONHCH 2   CH 2   —)}, 2.34 (1H, m, 2-CHb), 2.27 {6H, s, —N(CH 3 ) 2 }, 2.23-2.13 (2H, m, 2-CHa and 6-CHb), 2.03-1.84 (2H, m, 15-CH and 6-CHa), 1.58 (1H, dd, 1-CHb), 1.21 (1H, m, 1-CHa), 1.07 (3H, s, 20-CH 3 ), 0.99 (3H, d, 17-CH 3 ), 0.85 (3H, d, 16-CH 3 ) ppm. 
     Example 8 
     Synthesis of Triptolide 14-Ethyl Carbonate (PG674) 
     
       
         
         
             
             
         
       
     
     Using General Procedure C, the product was obtained in 89.6% yield from ethyl chloroformate and triptolide. Analytical TLC Rf=0.58 (ethyl acetate/hexanes/methanol 1:1:0.1). IR (KBr): 2972.3, 2938.3, 2879.4, 1474.3, 1677.0, 1448.0, 1372.0, 1253.5, 1170.1, 1092.8, 1068.5, 1004.4, 962.3, 912.3, 864.6, 786.0, 560.1 cm −1 . H 1  NMR (300 MHz, CDCl 3 ): δ=4.83 (1H, s, 14-CH), 4.68 (2H, q, 19-CH 2 ), 4.25 {2H, qd, 22-CH 2  (—O CH 2   CH 3 )}, 3.82 (1H, d, 11-CH), 3.55 (1H, dd, 12-CH), 3.49 (1H, d, 7-CH), 2.70 (1H, m, 5-CH), 2.32 (1H, m, 2-CHb), 2.19 (2H, m, 6-CHb and 2-CHa), 1.96 (2H, m, 15-CH and 6-CHa), 1.61 (1H, m, 1-CHb), 1.37 {3H, t, 23-CH 3  (—OCH 2   CH 3   )}, 1.21 (1H, m, 1-CHa), 1.07 (3H, s, 20-CH 3 ), 0.99 (3H, d, 17-CH 3 ), 0.86 (3H, d, 16-CH 3 ) ppm. 
     Example 9 
     Synthesis of Triptolide 14-Phenyl Carbonate (PG676) 
     
       
         
         
             
             
         
       
     
     Using General Procedure C, the product was obtained in 78.8% yield from phenyl chloroformate and triptolide. Analytical TLC Rf=0.53 (ethyl acetate/hexanes/methanol 1:1:0.1). IR (KBr): 2969.7, 2937.6, 1752.1, 1676.5, 1442.6, 1265.6, 1210.6, 1021.5, 961.8, 910.7, 774.3, 560.6 cm −1 . H 1  NMR (300 MHz, CDCl 3 ): δ=7.42-7.20 (5H, m, Ar—H), 4.83 (1H, s, 14-CH), 4.68 (2H, q, 19-CH 2 ), 3.83 (1H, d, 11-CH), 3.55 (1H, dd, 12-CH), 3.49 (1H, d, 7-CH), 2.68 (1H, m, 5-CH), 2.32 (1H, m, 2-CHb), 2.19 (1H, m, 6-CHb and 2-CHa), 1.96 (2H, m, 15-CH and 6-CHa), 1.49 (1H, m, 1-CHb), 1.24 (1H, m, 1-CHa), 1.07 (3H, s, 20-CH 3 ), 0.99 (3H, d, 17-CH 3 ), 0.86 (3H, d, 16-CH 3 ) ppm. 
     Example 10 
     Synthesis of Triptolide 14-Ethoxyethyl Carbonate (PG679) 
     
       
         
         
             
             
         
       
     
     Using General Procedure D, the product was obtained in 90.2% yield from triptolide, phosgene and ethoxyethanol. Analytical TLC Rf=0.49 (ethyl acetate/hexanes/methanol 1:1:0.1). IR (KBr): 2974.0, 2935.3, 2876.5, 1750.8, 1676.4, 1458.6, 1448.6, 1388.7, 1375.8, 1122.3, 1023.0, 962.3, 910.8, 866.1, 784.1, 751.6, 559.7 cm −1 . H 1  NMR (300 MHz, CDCl 3 ): δ=4.83 (1H, s, 14-CH), 4.80 (2H, q, 19-CH 2 ), 4.40 {1H, m, 22-CHb (OCOOCHa Hb CH 2 )}, 4.27 {1H, m, 22-CHa (OCOOC Ha HbCH 2 —)}, 3.82 (1H, d, 11-CH), 3.68 {2H, m, 23-CH 2  (OCOOCH 2   CH 2   —)}, 3.54 {3H, m, 12-CH and 24-CH 2  (—O CH 2   CH 3 )}, 3.48 (1H, d, 7-CH), 2.68 (1H, m, 5-CH), 2.31 (1H, m, 2-CHb), 2.18 (2H, m, 2-CHa and 6-CHb), 1.96 (2H, m, 15-CH and 6-CHa), 1.58 (1H, dd, 1-CHb), 1.21 {4H, 1-CHa and 25-CH 3  (OCH 2   CH 3   )}, 1.07 (3H, s, 20-CH 3 ), 0.99 (3H, d, 17-CH 3 ), 0.85 (3H, d, 16-CH 3 ) ppm. 
     Example 11 
     Synthesis of Triptolide 14-(R)-α-Methyl-tert-butoxycarbonylmethyl Carbonate (PG681) 
     
       
         
         
             
             
         
       
     
     Using General Procedure D, the product was obtained in 76.2% yield from triptolide, phosgene and tert-butyl (R)-(+)-lactate. Analytical TLC Rf=0.62 (ethyl acetate/hexanes/methanol 1:1:0.1). IR (KBr): 2979.5, 2938.3, 2880.6, 1754.6, 1676.9, 1474.0, 1458.1, 1370.1, 1351.6, 1318.0, 1264.2, 1165.7, 1136.2, 1116.3, 1074.7, 1031.2, 962.5, 912.6, 866.8, 843.6, 786.2, 560.6 cm −1 . H 1  NMR (300 MHz, CDCl 3 ): δ=4.85 {1H, q, 22-CH [OCOO CH (CH 3 )CO]}, 4.83 (1H, s, 14-CH), 4.68 (2H, q, 19-CH 2 ), 3.83 (1H, d, 11-CH), 3.56 (1H, dd, 12-CH), 3.48 (1H, d, 7-CH), 2.65 (1H, m, 5-CH), 2.31 (1H, m, 2-CHb), 2.23-2.04 (3H, m, 6-CHb, 2-CHa and 15-CH), 1.93 (1H, dd, 6-CHa), 1.59 (1H, dd, 1-CHb), 1.52 {3H, d, 28-CH 3  [OCOOCH( CH 3   )CO]}, 1.45 {9H, s, OC(CH 3 ) 3 }, 1.19 (1H, m, 1-CHa), 1.08 (3H, s, 20-CH 3 ), 1.01 (3H, d, 17-CH 3 ), 0.87 (3H, d, 16-CH 3 ) ppm. 
     Example 12 
     Synthesis of Triptolide 14-Methoxycarbonylmethyl Carbonate (PG680) 
     
       
         
         
             
             
         
       
     
     Using General Procedure D, the product was obtained in 82.4% yield from triptolide, phosgene and methyl glycolate. Analytical TLC Rf=0.45 (ethyl acetate:hexanes:methanol 1:1:0.1). IR (KBr): 2967.9, 2882.3, 1751.9, 1676.6, 1439.5, 1383.0, 1283.9, 1245.5, 1213.3, 1022.0, 1005.0, 962.1, 910.7, 783.1, 560.6, 547.9, 530.6, 521.5, 478.7 cm −1 . H 1  NMR (300 MHz, CDCl 3 ): δ=4.84 (1H, s, 14-CH), 4.80 {1H, d, 22-CHb (OCOOCHa Hb CO)}, 4.68 (2H, q, 19-CH 2 ), 4.57 {1H, d, 22-CHa (OCOOC Ha HbCO)}, 3.83 (1H, d, 11-CH), 3.79 {3H, s, 24-CH 3  (—OCH 3 )}, 3.56 (1H, dd, 12-CH), 3.49 (1H, d, 7-CH), 2.70 (1H, m, 5-CH), 2.32 (1H, m, 2-CHb), 2.23-2.14 (2H, m, 2-CHa and 6-CHb), 2.07-1.89 (2H, m, 15-CH and 6-CHa), 1.59 (1H, m, 1-CHb), 1.23 (1H, m, 1-CHa), 1.08 (3H, s, 20-CH 3 ), 1.02 (3H, d, 17-CH 3 ), 0.89 (3H, d, 16-CH 3 ) ppm. 
     Example 13 
     Synthesis of Triptolide 14-Dimethylaminoethyl Carbonate (PG682) 
     
       
         
         
             
             
         
       
     
     Using General Procedure D, the product was obtained in 71.2% yield from triptolide, phosgene and dimethylaminoethanol. Analytical TLC Rf=0.24 (ethyl acetate:hexanes:methanol:triethylamine 1:1:0.1:0.02). IR (KBr): 2969.4, 2824.8, 2772.3, 1751.1, 1676.2, 1671.3, 1655.0, 1473.9, 1466.0, 1375.1, 1254.9, 1020.4, 992.6, 962.7, 910.6, 778.9, 557.4, 517.1, 472.4, 440.7 cm −1 . H 1  NMR (300 MHz, CDCl 3 ): δ=4.83 (1H, s, 14-CH), 4.68 (2H, s, 19-CH 2 ), 4.34 {2H, m, 22-CH 2  (OCOO CH 2   CH 2 N)}, 3.82 (1H, d, 11-CH), 3.55 (1H, d, 12-CH), 3.49 (1H, d, 7-CH), 2.75-2.62 {3H, m, 23-CH 2  (OCOOCH 2   CH 2   N) and 5-CH}, 2.37 (6H, s, —N(CH 3 ) 2 }, 2.31 (1H, m, 2-CHb), 2.23-2.15 (2H, m, 2-CHa and 6-CHb), 2.04-1.89 (2H, m, 15-CH and 6-CHa), 1.58 (1H, dd, 1-CHb), 1.21 (1H, m, 1-CHa), 1.06 (3H, s, 20-CH 3 ), 0.99 (3H, d, 17-CH 3 ), 0.85 (3H, d, 16-CH 3 ) ppm. HRMS (FAB) m/z calcd for C 25 H 34 NO 8   +  (MH + ) 476.2284. found 476.2289. 
     Example 14 
     Synthesis of p-Toluenesulfonate Salt of Triptolide 14-Dimethylaminoethyl Carbonate (PG682 PTSA) 
     
       
         
         
             
             
         
       
     
     With stirring, to a solution of p-toluenesulfonic acid (19.0 mg, 0.10 mmol) in H 2 O (8.0 ml) was slowly added triptolide 14-dimethylaminoethyl carbonate (PG682) (47.6 mg, 0.10 mmol). After the addition, the solution was stirred for another 30 minutes and then lyophilized to yield 60.5 mg (93.4%) of white powder. IR (KBr): 3445.0, 3035.8, 2972.1, 2730.1, 1750.9, 1676.1, 1671.9, 1664.8, 1655.4, 1638.1, 1459.3, 1256.2, 1169.3, 1121.7, 1033.3, 1010.3, 961.0, 910.7, 817.9, 683.0, 570.4, 479.0 cm −1 . H 1  NMR (300 MHz, DMSO-d 6 ): δ=7.47 (2H, d, Ar—H), 7.10 (2H, d, Ar—H), 4.82 (2H, q, 19-CH 2 ), 4.80 (1H, s, 14-CH), 4.46 {2H, m, 22-CH 2  (OCOO CH 2   CH 2 N)}, 3.97 (1H, d, 11-CH), 3.73 (1H, d, 12-CH), 3.67 (1H, d, 7-CH), 3.44 {2H, m, 23-CH 2  (OCOOCH 2   CH 2   N)}, 2.83 (3H, s, Ar—CH 3 ), 2.63 (1H, m, 5-CH), 2.28 {6H, s, —N(CH 3 ) 2 }, 2.22 (1H, m, 6-CHb), 2.15 (1H, m, 2-CHb), 2.09 (1H, m, 2-CHa), 1.98 (1H, m, 1-CHb), 1.90 (1H, m, 15-CH), 1.81 (1H, dd, 6-CHa), 1.30 (1H, m, 1-CHa), 0.91 (3H, s, 20-CH 3 ), 0.90 (3H, d, 17-CH 3 ), 0.78 (3H, d, 16-CH 3 ) ppm. 
     Example 15 
     Synthesis of Triptolide 14-Hydroxycarbonylmethyl Carbonate (PG687) 
     
       
         
         
             
             
         
       
     
     Using General Procedure D, the product was obtained in 47.8% yield from triptolide, phosgene and glycolic acid. Analytical TLC Rf=0.32 (ethyl acetate:hexanes:methanol:acetic acid 1:1:0.1:0.1). IR (KBr): 3416.0, 2975.4, 1752.6, 1701.4, 1685.8, 1638.3, 1559.5, 1415.9, 1257.7, 1021.3, 810.3, 643.0, 528.0 cm −1 . H 1  NMR (300 MHz, MeOH-d 4 ): δ=4.85 (1H, s, 14-H), 4.82 {2H, q, 22-CH 2  (OCOO CH 2   CO)}, 4.46 (2H, q, 19-CH 2 ), 3.95 (1H, d, 11-CH), 3.65 (1H, d, 12-CH), 3.50 (1H, d, 7-CH), 2.78 (1H, m, 5-CH), 2.34-2.20 (2H, m, 6-CHb and 2-CHb), 2.08 (1H, m, 15-CH), 1.99-1.62 (2H, m, 2-CHa and 6-CHa), 1.50 (1H, dd, 1-CHb), 1.34 (1H, td, 1-CHa), 1.04 (3H, s, 20-CH 3 ), 0.98 (3H, d, 17-CH 3 ), 0.85 (3H, d, 16-CH 3 ) ppm. HRMS (FAB) m/z calcd for C 23 H 26 NaO 10   +  (MNa + ) 485.1424. found 485.1434. 
     Example 16 
     Synthesis of Sodium Salt of Triptolide 14-Hydroxycarbonylmethyl Carbonate (PG687 Na) 
     
       
         
         
             
             
         
       
     
     To a solution of NaHCO 3  (5.18 mg, 0.0616 mmol) in H 2 O (3.9 ml) was slowly added triptolide 14-hydroxycarbonylmethyl carbonate (PG687) (28.5 mg, 0.0616 mmol) with stirring. After the addition, the solution was stirred for another 30 minutes and then lyophilized to yield 29.7 mg (99.3%) of white powder. IR (KBr): 2961.4, 2877.2, 1638.1, 1560.8, 1551.2, 1412.0, 1261.8, 1021.0, 803.4, 641.0, 530.6, 523.5 cm −1 . H 1  NMR (300 MHz, DMSO-d 6 ): δ=4.82 {2H, q, 22-CH 2  (OCOO CH 2   CO)}, 4.70 (1H, s, 14-CH), 4.16 (1H, d, 19-CHb), 3.98 (1H, d, 19-CHa), 3.94 (1H, d, 11-CH), 3.69 (1H, d, 12-CH), 3.57 (1H, d, 7-CH), 2.58 (1H, m, 5-CH), 2.22 (1H, m, 6-CHb), 2.11 (1H, m, 2-CHb), 1.97 (2H, m, 2-CHa and 15-CH), 1.81 (1H, m, 6-CHa), 1.49 (1H, m, 1-CHb), 1.30 (1H, m, 1-CHa), 0.92 (3H, s, 20-CH 3 ), 0.90 (3H, d, 17-CH 3 ), 0.75 (3H, d, 16-CH 3 ) ppm. 
     Example 17 
     Synthesis of Tris(hydroxymethyl)aminomethane Salt of Triptolide 14-Hydroxycarbonyl-methyl Carbonate (PG687 tris) 
     
       
         
         
             
             
         
       
     
     To a suspension of triptolide 14-hydroxycarbonylmethyl carbonate (PG687) (8.3 mg, 0.018 mmol) was added a solution of tris(hydroxymethyl)aminomethane (2.17 mg, 0.018 mmol) in H 2 O (0.75 ml) with stirring. After the addition, the solution was stirred for another 30 minutes and then lyophilized. The powder was dissolved in H 2 O (2.0 ml) and filtered through a pad of cotton to remove the fine particles. The filtrate was then lyophilized to yield 10.1 mg (96.5%) of white powder. IR (KBr): 3364.5 (br), 2975.8, 1750.1, 1581.1, 1413.7, 1349.8, 1255.7, 1019.0, 968.5, 911.1, 648.9, 619.6, 561.2, 497.8 cm −1 . H 1  NMR (300 MHz, DMSO-ds): δ=4.82 {2H, q, 22-CH 2  (OCOO CH 2   CO)}, 4.70 (1H, s, 14-CH), 4.20 (1H, d, 19-CHb), 4.02 (1H, d, 19-CHa), 3.94 (1H, d, 11-CH), 3.69 (1H, d, 12-CH), 3.56 (1H, d, 7-CH), 3.20 (6H, s, (HO CH 2   ) 3 CNH 2 }, 2.61 (1H, m, 5-CH), 2.22 (1H, m, 6-CHb), 2.11 (1H, m, 2-CHb), 1.96 (2H, m, 2-CHa and 15-CH), 1.81 (1H, m, 6-CHa), 1.30 (2H, m, 1-CH 2 ), 0.91 (3H, s, 20-CH 3 ), 0.90 (3H, d, 17-CH 3 ), 0.76 (3H, d, 16-CH 3 ) ppm. 
     Example 18 
     Synthesis of Triptolide 14-tert-Butyl Carbonate (PG695) 
     
       
         
         
             
             
         
       
     
     To a solution of triptolide (108.1 mg, 0.30 mmol, 1.0 eq) and 4-DMAP (367.0 mg, 3.0 mmol, 10.0 eq) in dichloromethane (15 ml) was added with stirring di-tert-butyl dicarbonate (393.0 mg 1.80 mmol, 6.0 eq) at room temperature under nitrogen. After 48 hours of stirring at room temperature, methyl alcohol (1.0 ml) was added. The reaction mixture was concentrated under vacuum and the crude product was purified with preparative TLC (ethyl acetate/hexanes/methanol 1:1:0.1) to give 131.3 mg (95.1%) of the desired product. Analytical TLC Rf=0.66 (ethyl acetate/hexanes/methanol 1:1:0.1). IR (KBr): 2976.7, 2938.5, 1738.2, 1676.7, 1444.6, 1394.6, 1370.5, 1335.2, 1278.4, 1254.5, 1160.1, 1118.2, 1091.8, 1020.2, 991.6, 962.9, 912.0, 854.4, 786.4, 751.5, 607.2, 558.2, 529.3, 478.2 cm −1 . H 1  NMR (300 MHz, CDCl 3 ): δ=4.80 (1H, s, 14-CH), 4.68 (2H, q, 19-CH 2 ), 3.81 (1H, d, 11-CH), 3.53 (1H, d, 12-CH), 3.46 (1H, d, 7-CH), 2.69 (1H, m, 5-CH), 2.35 (1H, m, 2-CHb), 2.18 (2H, m, 6-CHb and 2-CHa), 1.96 (2H, m, 15-CH and 6-CHa), 1.61 (1H, m, 1-CHb), 1.51 {9H, s, —OC(CH 3 ) 3 }, 1.24 (1H, m, 1-CHa), 1.08 (3H, s, 20-CH 3 ), 0.99 (3H, d, 17-CH 3 ), 0.86 (3H, d, 16-CH 3 ) ppm. 
     Example 19 
     Apoptosis Assays 
     A. Incubation of compounds with human serum. Pooled human serum was stored in aliquots at −80° C. Test compounds were added at 20 mM to thawed human serum in 1.5 ml microfuge tubes and incubated at 37° C. in a water bath for varying periods of time. The test samples were placed on ice until dilution for the bioassay. Controls consisted of the compounds incubated in complete tissue culture medium (RPMI 1640 medium plus 5% heat-inactivated fetal calf serum, 1% HEPES, 1% pen/strep, 1% glutamine) rather than human serum. 
     B. Apoptosis assay of compounds incubated with human serum. Test samples were diluted to 1 mM in complete tissue culture medium. Aliquots were placed in microculture plates and serial dilutions were prepared so that the final concentration would encompass the range of 1 to 10,000 nM with half-log increments. Cells from an exponentially expanding culture of the Jurkat human T lymphocyte cell line (#TIB-152 obtained from American Type Culture Collection, Manassas, Va.) were harvested, washed once by centrifugation and dilution in complete tissue culture medium, and diluted to a concentration of 1×10 6  cells/ml. A volume of 100 μl of Jurkat cells (1×10 5  cells) was added to wells containing 100 μl of the diluted compounds, and the plates were incubated at 37° C. in a 5% CO 2  incubator. After 24 hours, the plates were centrifuged to pellet the cells, and the cells were washed twice with 2% heat-inactivated fetal calf serum in PBS. To each well, 500 ul of binding buffer was added according to the Annexin V assay procedure (BioVision, Inc., Mountain View, Calif.). Next, 5 μl of the fluorescein isothiocyanate (FITC) conjugate of Annexin V (BioVision, Inc.) was added to each well, followed by 5 minutes of incubation in the dark. In some assays, propidium iodide (BioVision, Inc.) was added at this stage to check for necrotic cells. The contents of the wells were individually transferred into test tubes, and apoptosis was analyzed using a FACSCalibur flow cytometer (BD Immunocytometry Systems, San Jose, Calif.). Cells positive for Annexin V binding were considered to be apoptotic, and the data were calculated as percent apoptotic cells. 
     C. Comparison of bioactivities after incubation of compounds in human serum. The data were plotted as the concentration of compound incubated in serum versus percent apoptotic cells. The concentration of compound inducing 50% apoptosis (ED 50 ) was calculated from these dose response curves. The percent conversion of the test compounds to bioactive compounds (assumed to be triptolide) was calculated in reference to the result with triptolide incubated in parallel in human plasma in the same experiment, as the percent of the ED 50  of the compound compared to that for triptolide, which was taken as 100%. This percentage conversion was used to compare the bioactivity of various compounds after incubation in human serum. 
     Example 20 
     Immunosuppression Assays 
     A. IL-2 production assay for activity of compounds incubated with human serum. Test samples were diluted to 1 mM in complete tissue culture medium. Aliquots were placed in microculture plates that had been coated with anti-CD3 antibody (used to stimulate the production of IL-2 by Jurkat cells) and serial dilutions were prepared so that the final concentration would encompass the range of 0.001 to 10,000 nM in log increments. Cells from an exponentially expanding culture of the Jurkat human T lymphocyte cell line (#TIB-152 obtained from American Type Culture Collection, Manassas, Va.) were harvested, washed once by centrifugation and dilution in complete tissue culture medium, and diluted to a concentration of 2×10 6  cells/ml. A volume of 50 μl of Jurkat cells (1×10 5  cells) was added to wells containing 100 μl of the diluted compounds, 50 μl of PMA (10 ng/ml) was added to each well, and the plates were incubated at 37° C. in a 5% CO 2  incubator. After 24 hours, the plates were centrifuged to pellet the cells, 150 μl of supernatant was removed from each well, and the samples were stored at −20° C. The stored supernatants were analyzed for human IL-2 concentration using the Luminex 100 (Luminex Corporation, Austin, Tex.), Luminex microspheres coupled with anti-IL-2 capture antibody, and fluorochrome-coupled anti-IL-2 detection antibody. The data were expressed as ng/ml of IL-2. 
     B. Comparison of bioactivities after incubation of compounds in human serum. The data were plotted as the concentration of compound incubated in serum versus IL-2 concentration. The concentration of compound inducing a 50% decrease in the IL-2 concentration (IC 50 ) was calculated from these dose response curves. The percent conversion of the test compounds to bioactive compounds (assumed to be triptolide) was calculated in reference to the result with triptolide incubated in parallel in human plasma in the same experiment, as the percent of the IC 50  of the compound compared to that for triptolide, which was taken as 100%. This percentage conversion was used to compare the bioactivity of various compounds after incubation in human serum.