Abstract:
The present invention provides certain 6-hetarylalkyloxy pyrimidine derivatives of formula II ##STR1## wherein R is (i) a cyclic group having at least one 5- or 6-membered heterocyclic ring, optionally with a carbocyclic or heterocyclic ring fused thereto, the or each heterocyclic ring having at least one hetero atom chosen from O, N, or S, or a substituted derivative thereof; or (ii) phenyl or a substituted derivative thereof, 
     R 2  is selected from H, C 1  -C 5  alkyl, halogen or NH 2 , 
     R 4  and R 5  which are the same or different are selected from 
     H, NH 2  or NO n  where n=1 or 2, or R 4  and R 5  together with the pyrimidine ring form a 5-or 6-membered ring structure containing one or more heterocyclic atoms, and pharmaceutically acceptable salts thereof, exhibit the ability to deplete O 6  -alkylguanine-DNA alkyltransferase (ATase) activity.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of application Ser. No. 08/568,576 entitled &#34;O 6  -subsituted guanine derivatives, a process for their preparation and their use in treating tumour cells&#34; filed 7 Dec. 1995 which in turn is a continuation-in-part of International Application PCT/IE94/00031, with an international filing date of 8 Jun. 1994. 
    
    
     TECHNICAL FIELD 
     The present invention relates to 6-hetarylalkyloxy pyrimidine derivatives, a process for their preparation and their use in treating tumour cells. In particular, it relates to pyrimidine derivatives having hetarylalkyloxy substituents in the 6-position, these compounds exhibiting the ability to deplete O 6  -alkylguanine-DNA alkyltransferase (ATase) activity in tumour cells. 
     BACKGROUND ART 
     It has been suggested to use O 6  -alkyl guanine derivatives possessing O 6  -alkylguanine-DNA alkyltransferase depleting activity in order to enhance the effectiveness of chemotherapeutic alkylating agents used for killing tumour cells. There is increasing evidence that in mammalian cells the toxic and mutagenic effects of alkylating agents are to a large extent a consequence of alkylation at the O 6  -position of guanine in DNA. The repair of O 6  -alkylguanine is mediated by ATase, a repair protein that acts on the O 6  -alkylated guanine residues by stoichiometric transfer of the alkyl group to a cysteine residue at the active site of the repair protein in an autoinactivating process. The importance of ATase in protecting cells against the biological effects of alkylating agents has been most clearly demonstrated by the transfer and expression of cloned ATase genes or cDNAs into ATase deficient cells; this confers resistance to a variety of agents, principally those that methylate or chloroethylate DNA. Whilst the mechanism of cell killing by O 6  -methylguanine in ATase deficient cells is not yet clear, killing by O 6  -chloroethylguanine occurs through DNA interstrand crosslink formation to a cytosine residue on the opposite strand via a cyclic ethanoguanine intermediate, a process that is prevented by ATase-mediated chloroethyl group removal or complex formation. 
     The use of O 6  -methylguanine and O 6  -n-butylguanine for depleting ATase activity has been investigated (Dolan et al., Cancer Res., (1986) 46, pp. 4500; Dolan et al., Cancer Chemother. Pharmacol., (1989) 25. pp 103. O 6  -benzylguanine derivatives have been proposed for depleting ATase activity in order to render ATase expressing cells more susceptible to the cytotoxic effects of chloroethylating agents (Moschel et al., J. Med.Chem., 1992, 35, 4486). U.S. Pat. No. 5,091,430 and International Patent Application No. WO 91/13898 Moschel et al. disclose a method for depleting levels of O 6  -alkylguanine-DNA alkyl-transferase in tumour cells in a host which comprises administering to the host an effective amount of a composition containing O 6  -benzylated guanine derivatives of the following formula: ##STR2## wherein Z is hydrogen, or ##STR3## and R a  is a benzyl group or a substituted benzyl group. A benzyl group may be substituted at the ortho, meta or para position with a substituent group such as halogen, nitro, aryl such as phenyl or substituted phenyl, alkyl of 1-4 carbon atoms, alkoxy of 1-4 carbon atoms, alkenyl of up to 4 carbon atoms, alkynyl of up to 4 carbon atoms, amino, monoalkylamino, dialkylamino, trifluoromethyl, hydroxy, hydroxymethyl, and SO n  R b  wherein n is 0, 1, 2 or 3 and R b  is hydrogen, alkyl of 1-4 carbon atoms or aryl. Mi-Young Chae et al, J.Med.Chem., 1994, 37, 342-347 describes tests on O 6  -benzylguanine analogs bearing increasingly bulky substituent groups on the benzene ring or at position 9. Mi-Young Chae et. al., J. Med. Chem. 1995, 38, 359-365 published on 20 Jan. 1995 describe several 8-substituted O 6  -benzylguanines, 2- and/or 8-substituted 6-(benzyloxy)purines, substituted 6(4)-(benzyloxy)pyrimidines, and a 6-(benzyloxy)-s-triazine which were tested for their ability to inactivate ATase . Two types of compounds were identified as being significantly more effective than O 6  -benzylguanine at activating ATase in human HT29 colon tumour cell extracts. These were 8-substituted O 6  -benzylguanines bearing electron-withdrawing groups at the 8-position (e.g. 8-aza-O 6  -benzylguanine and O 6  -benzyl-8-bromoguanine) and 5-substituted 2,4-diamino-6-(benzyloxy)pyrimidines bearing electron withdrawing groups at the 5-position (e.g. 2,4-diamino 6-(benzyloxy)-5-nitroso- and 2,4-diamino-6-(benzyloxy)-5-nitropyrimidine). The latter derivatives were also more effective than O 6  -benzylguanine at inactivating ATase in intact HT29 colon tumour cells. 
     The present inventors are also inventors in U.S. patent application Ser. No. 08/568,576, entitled &#34;O 6  -substituted guanine derivatives, a process for their preparation and use thereof in treating tumour cells&#34; filed 7 Dec. 1995 as a Continuation-In-Part of International Application PCT/IE94/00031 which has an international filing date of 8 Jun. 1994 and which was published under No. WO 94/29312 on 22 Dec. 1994. The U.S. Application and WO 94/29312 (the contents of which are incorporated herein by reference in their entirety) describe O 6  -substituted guanine derivatives of formula I: ##STR4## wherein 
     Y is H, ribosyl, deoxyribosyl, or R&#34;XCHR&#39;&#34;, wherein X is O or S, R&#34; and R&#39;&#34; are alkyl, or substituted derivatives thereof; 
     R&#39; is H, alkyl or hydroxyalkyl; 
     R is (i) a cyclic group having at least one 5- or 6-membered heterocyclic ring, optionally with a carbocyclic or heterocyclic ring fused thereto, the or each heterocyclic ring having at least one hetero atom chosen from O, N, or S, or a substituted derivative thereof; or 
     (ii) naphthyl or a substituted derivative thereof; 
     and pharmaceutically acceptable salts thereof. 
     It is an object of the present invention to provide novel compounds useful for depleting ATase activity in order to enhance the effects of chemotherapeutic agents such as chloroethylating or methylating anti-tumour agents. It is a further object to provide compounds having better ATase inactivating characteristics than O 6  -benzylguanine and having different solubility patterns. 
     Another object of the invention is to provide pharmaceutical compositions containing compounds which are useful for depleting ATase activity. A further object of the present invention is to provide a method for depleting ATase activity in tumour cells. A still further object of the invention is to provide a method for treating tumour cells in a host. 
     The present invention provides 6-hetarylalkyloxy pyrimidine derivatives of formula II ##STR5## wherein 
     R is as defined in (i) above, or R is phenyl or a substituted derivative thereof, 
     R 2  is selected from H, C 1  -C 5  alkyl, halogen or NH 2 , R 4  and R 5  which are the same or different are selected from H, NH 2  or NO n  where n 1 or 2, or R 4  and R 5  together with the pyrimidine ring form a 5- or 6-membered ring structure containing one or more hetero atoms, and pharmaceutically acceptable salts thereof, 
     provided that R 2  is not NH 2  if R 4  and R 5  form a ring structure IX ##STR6## 
     wherein Y is H, ribosyl, deoxyribosyl, arabinosyl, or R&#34;XCHR&#39;&#34; wherein X is O or S, R&#34;&#34; and R&#39;&#34; are alkyl, or subsituted derivatives thereof, and provided that R is not phenyl; 
     a) if R 2  and R 5  are NH 2  and R 4  is NO or NO 2   
     b) if R 2  is NH 2  and R 4  and R 5  form a ring structure X ##STR7## c) if R 2  is NH 2  and R 4  and R 5  for a ring structure XI ##STR8## d) if R 2  is NH 2 , R 4  is NO 2  and R 5  is H or CH 3   
     e) if R 2 , R 4  and R 5  are NH 2 . 
     f) if R 2  and R 5  are NH 2  and R 4  is H 
     g) if R 2  is H, R 4  is NO 2  and R 5  is NH 2   
     h) if R 2  is F or OH, and R 4  and R 5  form a ring structure XII ##STR9## 
     R may suitably be a 5- or 6-membered heterocyclic ring or a benzo derivative thereof, in which latter case the 6-alkyloxypyrimidine moiety may be attached to R at either the heterocyclic or the benzene ring. 
     In preferred embodiments, R is a 5-membered ring containing S or O, with or without a second ring fused thereto. 
     Preferably, R is a heterocyclic ring having at least one S atom; more preferably, R is a 5-membered heterocyclic ring having at least one S atom; and most preferably, R is a thiophene ring or a substituted derivative thereof. 
     Alternatively, R may be a heterocyclic ring having at least one O atom, particularly, a 5-membered heterocyclic ring having at least one O atom and more particularly R may be a furan ring or a substituted derivative thereof. 
     As another alternative, R may be a heterocyclic ring having at least one N atom, particularly R may be a 6-membered heterocyclic ring having at least one N atom and in particular, R may be a pyridine ring. 
     In the definition of Y, the term &#34;substituted derivative&#34; includes substitution by one or more of the following groups: hydroxy, halo, alkoxy, amino, alkylamino, amido or ureido. 
     In the definition of R, the term &#34;substituted derivative&#34; includes substitution of the heterocyclic rings and/or carbocyclic ring(s) by one or more of the following groups: alkyl, alkenyl, alkynyl, halo, haloalkyl, nitro, cyano, hydroxyalkyl, SO n  R&#34;&#34; where R&#34;&#34; is alkyl and n=0,1 or 2, or a carboxyl or ester group of the formula --COOR 5  wherein R 5  is H or alkyl. Halo, haloalkyl, cyano, alkylenedioxy SO n  R&#34;&#34; (as defined above) and --COOR 5  wherein R 5  is alkyl are preferred substituents. 
     An alkyl, alkenyl, or alkynyl group preferably contains from 1 to 20, more preferably from 1 to 10 and most preferably from 1 to 5 carbon atoms. Halo includes iodo, bromo, chloro or fluoro. 
     One embodiment of the invention provides a pharmaceutical composition containing compounds of formula II, wherein Y, R, R 2 , R 4  and R 5  are as defined above, or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable excipient. Optionally the composition may also contain an alkylating agent such as a chloroethylating or methylating agent. 
     In a further embodiment, the present invention provides a method for depleting Abase activity in a host comprising administering to the host an effective amount of a composition containing a compound of formula II wherein Y, R, R 2 , R 4  and R 5  are as defined above, or a pharmaceutically acceptable salt thereof, more particularly a pharmaceutical composition as defined above. This method may alternatively be defined as a method of depleting ATase mediated DNA repair activity in a host. 
     The invention further provides a method for treating tumour cells in a host comprising administering to the host an effective amount of a composition containing a compound of formula II wherein Y, R, R 2 , R 4  and R 5  are as defined above or a pharmaceutically acceptable salt thereof, more particularly a pharmaceutical composition as defined above and administering to the host an effective amount of a composition containing an alkylating agent. The method may be used for treatment of neoplasms including those which are known to be sensitive to the action of alkylating agents e.g. melanoma and glioma and others whose resistance to treatment with alkylating agents alone may be overcome by the use of an inactivator according to the invention. 
     Subject to the provisos above the preferred compounds of the invention are those of: ##STR10## wherein: 
     R is as defined for formula II, particularly furyl or thienyl unsubstituted or substituted, preferahly with a halogen such as chlorine, bromine or fluorine, 
     Y is H or HOCH 2  CH 2  OCH 2  -; 
     R 2  is H, NH 2 , C 1  -C 5  alkyl, preferably methyl, or halogen, preferably fluorine; 
     R 3  is H or OH; ##STR11## wherein: 
     R is as defined for formula II, particularly phenyl, thienyl or furyl unsubstituted or substituted preferably with a halogen such as chlorine, bromine or fluorine, or phenyl having a methylenedioxy ring structure fused thereto; 
     Y is as defined for formula II; 
     X is CH or N; 
     A is CH or N; and preferably when X=N, A=CH ##STR12## wherein: 
     R is as defined for formula II 
     X is CH or N 
     A is CH or N; ##STR13## wherein: 
     R is as defined for formula II, particularly phenyl, thienyl or furyl unsubstituted or substituted preferably with a halogen such as chlorine or bromine; 
     Z is O or S or CH═CH; ##STR14## wherein: 
     R is as defined for formula II; 
     U is CH or N; 
     V is CH or N; 
     W is CH or N; ##STR15## wherein: 
     R is as defined for formula II, particularly phenyl optionally substituted with halogen preferably one or more of chlorine, fluorine or bromine, or methylenedioxy; thenyl or furyl optionally substituted with halogen preferably one or more of chlorine, bromine or fluorine; 
     T is H, NH 2  or NO n  where n-=1 or 2; 
     Q is H, NH 2  or NO n  where n=1 or 2; 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Examples of compound of the invention are shown in Tables 1a and 1b. They were synthesized by the procedures presented below, adapted as appropriate. 
     Type 1 
     A. O 6  -Substituted hypoxanthines were made by the action of alkoxide RCH 2  ONa on the quaternary salt N,N,N-trimethyl-1H-purin-6-aminium chloride. 1   
     B. O 6  -Substituted 2-methylhypoxanthines were made similarly, from the quaternary salt from diazabicyclooctane (DABCO) and 6-chloro-2-methylpurine. 2 . 
     C. O 6  -Substituted 2-fluorohypoxanthines were made by diazolisation of the corresponding guanines using sodium nitrite and concentrated fluoboric acid at -25° C. 3   
     D. O 6  -Substituted 9-(2-hydroxyethoxymethyl)guanines were made by condensing the corresponding guanines after silylation with 2-acetoxyethoxymethyl bromide in the presence of mercuric cyanide followed by saponificationb of the O-acetyl group. 4   
     E. O 6  -Substituted 8-hydroxyguanines were made from 6-hetarylmethyl-2,4,5-triaminopyrimidines and 1, 1-carbonyldiimidazole in DMF. 5  Reaction of 6-chloro-2,4-diaminopyrimidine with alkoxide in DMSO, followed by nitrosation with sodium nitrite in aqueous acetic acid and reduction using sodium hydrosulphite in aqueous DMF, fave the 2, 4, 5-triamines. 
     Type 2 
     O 6  -Substituted 8-azaguanines were made from the above triamines and sodium nitrite in aqueous acetic acid. 6   
     B. O 6  -Substituted 8-aza-7-deazaguanines were made from the alkoxide RCH 2  ONa and 2-amino-6-chloro-8-aza-7-deazapurine 7  in sulfolane or from the DABCO quaternary salt (in DMSO solvent) derived from it. 
     Type 3 
     A. O 6  -Substituted 8-oxaguanines were made by lead tetraacetate oxidation 8  of 6-hetarylmethyl-2,4-diamino-5-nitrosopyrimidines obtained as under Type IE. 
     B. O 6  -Substituted 8-thiaguanines were made from the triamine intermediates under Type IE and N-tosylthionylimine in pyridine. 9   
     C. O 4  -Substituted pterins were made from these triamines and glyoxal with sodium metabisulphite.  10   
     Type 4 
     A and B. These pyrimidines were obtained as under Type IE. 
     C. O 6  -Substituted 2,4-diamino-5-nitropyrimidines were made by the action of alkoxide RCH 2  ONa in DMSO on 6-chloro-2,4-diamino -5-nitropyrimidine.  11   
     Compounds of formula II in which Y is R&#34;XCHR&#39;&#34;. (seco-nucleosides) may be prepared by an analogous preparation to the reaction of O 6  -benzylguanine with α-chloro-ethers (MacCoss et al., Tetrahedron Lett.; European Patent Application No. 184,473., loc. cit.) or with alkyl bromides (e.g. Kjellberg, Liljenberg and Johansson, Tetrahedron Lett., 1986, 27, 877; Moschel, McDougall, Dolan, Stine, and Pegg, J.Med. Chem., 1992, 35, 4486). 
     Typical &#34;sugar&#34; components corresponding to R&#34;XCHR&#39;&#34;, leading to seco-nucleosides, are made by methods described in e.g. McCormick and McElhinney, J. Chem. Soc., Perkin Trans. 1, 985, 93; Lucey, McCormick and McElhinney, J. Chem. Soc, Perkin Trans. 1, 1990, 795. 
     Compounds of formula II in which Y is ribosyl or deoxyribosyl (nucleosides) may be prepared by methods analogous to the syntheses of O 6  -benzylguanine riboside and 2-deoxyriboside (Moschel et al. 1992; cf. Gao, Fathi, Gaffney et al., J. Org. Chem., 1992, 57, 6954; Moschel, Hudgins and Dipple, J. Amer. Chem. Soc., 1981, 103, 5489) (see preparation of Ribosides above). 
     The amount of the compound of the present invention to be used varies according to the effective amount required for treating tumour cells. A suitable dosage is that which will result in a concentration of the compound of the invention in the tumor cells to be treated which results in the depletion of ATase activity, e.g. about 1-2000 mg/kg body weight, and preferably 1-800 mg/kg body weight, particularly 1-120 mg/kg body weight, prior to chemotherapy with an alkylating agent. 
     The pharmaceutical composition of the invention may be formulated in conventional forms with conventional excipients, as described for example in U.S. Pat. Nos. 5,091,430 and 5,352,669, the contents of which are incorporated herein by reference in their entirety. The composition may contain the inactivator according to the invention together with an alkylating agent; or the composition may comprise two parts, one containing the inactivator and the other containing the alkylating agent. The method of administering the compounds of the invention to a host may also be a conventional method, as described in U.S. Pat. Nos. 5,091,430 and 5,352,669 for example. For administration of an inactivator according to the invention to patients, the pharmaceutical composition may suitably contain the inactivator in a suitable vehicle such as 40% polyethyleneglycol 400 in saline solution, or in saline or 3% ethanol (in saline), for intravenous injection, or in a powder form in suitable capsules for oral administration. 
     Alkylating agents may be administered in accordance with known techniques and in conventional forms of administration, as described in U.S. Pat. Nos. 5,091,430 and 5,352,669 for example or preferably as a single dose immediately after or up to 24 hours after but preferably around 2 hours after administration of the ATase inactivating agents and also at doses lower than those used in standard treatment regimen. A reduction in dose may be necessary because the inactivators would generally be anticipated to increase the toxicity of the alkylating agents. Examples of chloroethylating agents include 1,3 bis (2-chloroethyl)-1-nitrosourea (BCNU), 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU), fotemustine, mitozolomide and clomesone and those described in McCormick, McElhinney, McMurry and Maxwell J. Chem. Soc, Perkin Trans. I, 1991, 877 and Bibby, Double, McCormick, McElhinney, Radacic, Pratesi and Dumont Anti-Cancer Drug Design, 1993, 8, 115. Examples of methylating agents include temozolomide U.S. Pat. No. 5,260,291 the contents of which are incorporated herein in their entirety) and dacarbazine, procarbazine, and streptozocin. 
     Method of Purification of Recombinant ATases 
     The cDNA cloning and overexpression of the human ATase has been reported previously 23 . Purification of the recombinant proteins was achieved either by affinity chromatography through a DNA-cellulose column as described by Wilkinson et al., 25 , 26, or by DEAE-cellulose ion-exchange chromatography. For the latter, the ATase protein was partially purified by ammonium sulphate precipitation (30-60%) and dialyzed against 10 mM Tris-HCl pH 7.5, 1 mM DTT, 2 mM EDTA, 10% glycerol, before loading on a DEAE-cellulose column. The ATase was then eluted with a 0-0.1 M NaCl gradient. The purified human ATase protein retained activity for more than one year when stored at high concentration at -20° C. in buffer I  50 mM-Tris/HCl (pH 8.3)3 mM-dithiothreitol/1 mM-EDTA! and could be thawed and refrozen several times without substantial loss of activity. 
     Incubation with Inactivators and ATase Assay 
     Compounds to be tested were dissolved in DMSO to a final concentration of 10 mM and diluted just before use in buffer I containing 1 mg/ml bovine serum albumin (IBSA). Recombinant ATase was diluted in IBSA and titrated in order that the reaction be conducted under ATase, and not substrate, limiting conditions. In each assay, fixed amounts of ATase (60-75 fmol) were incubated with varying amounts of O 6  -benzylguanine, or test compound in a total volume of 200 ul of IBSA containing 10 ug of calf thymus DNA at 37° C. for 1 hour. ATase substrate DNA was prepared by incubation of purified calf thymus DNA with N-  3  H!-methyl-N-nitrosurea (18.7 Ci/mmole, Amersham International). The   3  H!-methylated-DNA substrate (100 ul containing 6.7 ug of DNA and 100 fmol of O 6  -methylguanine) was added and incubation continued at 37° for 1 hour, until the reaction was completed. Following acid hydrolysis of the DNA as previously described 21  the   3  H!-methylated protein was recovered and quantitated by liquid scintillation counting. Samples were typically assayed in duplicate and experiments repeated several times. I 50  is the concentration of inactivator required to produce a 50% reduction in ATase activity. 
     Test Results 
     The results of the AT assay are shown in Table 2. Many of the compounds tested were more efficient in inactivating ATase than O 6  -benzylguanine. In accordance with the results in the parent application, compounds in which R is a heterocyclic group were more efficient than the comparable compounds having benzyloxy side chains. In general the compounds in which RCH 2  is substituted or unsubstituted thenyl were the most efficient, the most preferred being halo-substituted thenyl having its halo substituent in a 1,3-relationship with the methyleneoxy group attached to the pyrimidine residue. 
     Typical Synthetic Procedures 
     Type 1A. 
     O 6  -(4-Bromothenyl)hypoxanthine. B. 4292 
     4-Bromothenyl alcohol (1.16 g, 6 mmol) was added to sodium hydride (60% in oil; 0.16 g, 2 mmol) and DMSO (1 ml), The solution was stirred for 30 min. The trimethylammonium salt (0.427 g, 2 mmol) was then added and stirring continued for 2.5 h at 20° C. The solution was cooled in an ice bath and poured into ether (60 ml) containing acetic acid (0.32 ml). A white precipitate was collected, triturated with water (4 ml) and collected again to give B. 4292 (436 mg, 69%) recrystallised from methanol. 
     Type 1B. 
     O 6  -Thenyl-2-methylhypoxanthine, B. 4350 
     DABCO salt from 6-chloro-2-methylpurine: 
     6 chloro-2-methylpurine (0.5 g, 3 mmol) was dissolved in a mixture of DMF (5 ml) and diglyme (25 ml). DABCO (0.66 g, 6 mmol) was then added. The mixture was Stinfed for 1 h and the precipitate collected to give the quatenary salt (700 mg, 82%). NMR (300 MIIz, DMSO-d 6 ): shift in ppm 2.65 (s), 3.27 (t, J=7.5 Hz), 3.78 (s), 4.14 (t, J=7.5 Hz), 8.21 (s). 
     Thenyl alcohol (684 mg, 6 mmol) was added to sodium hydride (60% in oil; 80 mg, 2 mmol) and DMSO (0.5 ml). The solution was stirred for 30 min. The DABCO salt was then added and stirring continued for 5 h. The solution was then poured into ether (30 ml) containing acetic acid (0.15 ml). A precipitate was collected, triturated with water (4 ml) and collected again to give O 6  -Thenyl-2-methylhypoxanthine (96 mg, 35%) recrystallised from acetonitrile. 
     Type 1C. 
     O 6  -(4-Bromothenyl)-2-fluorohypoxanthine, B. 4353 
     To 3.6 ml of 40% fluoroboric acid precooled to -25° C. in a bath was added O 6  -(4-bromothenyl) guanine (326 mg, 1 mmol) with vigorous stirring. A solution of sodium nitrite (0.116 g, 1.7 mmol) in water (0.15 ml) was added dropwise over a period of 10 min. After 20 min, the solution was poured into ice. The mixture was then allowed to stand at 0° C. for 15 h, then collected and dried to afford almost pure (t.l.c.) B. 4353 (180 mg, 55%). Flash chromatography (Hexane--Ethyl Acetate decreasing polarity little by little) afforded B. 4353 
     Type 1D. 
     O 6  -(4-Bromothenyl)-9-(2-hydroxyethoxymethyl)guanine, B. 4335 
     A stirred mixture of O 6  -(4-Bromothenyl)guanine (294 mg, 1 mmol), (NH 4 ) 2  SO 4  (47 mg) and hexamethyldisilazane (5 ml) was heated at reflux for 3 h. Volatile material was then evaporated under vacuum. The residue was stirred with benzene (15 ml) and Hg(CN) 2  (344 mg, 1.3 mmol) under reflux for 30 min. A solution of (2-acetoxyethoxy)methyl bromide (197 mg, 1 mmol) in benzene (10 ml) was added, reflux maintained for 2 h, and the cloudy solution diluted with chloroform (150 ml). The organic phase was washed with saturated aqueous NaIICO 3  (30 ml), followed by KI (1M; 30 ml), dried over MgSO 4  and evaporated to give an oil (313 mg). This oil was chromatographed on a silica gel column with CHCl 3  -McOII (12:1) as eluant, yielding almost pure (t.l.c.) O-acetate (141 mg) of B. 4335. Methanol (60 ml) was saturated with dry ammonia and poured onto this O-acetate in a flask which was tightly stoppered. After dissolution, stirring was stopped and the flask left closed overnight. Evaporation of methanol gave B. 4335 (135 mg, 46%), recrystallised from isopropanol. 
     Type 1E. 
     O 6  -(4-Bromothenyl)-8-hydroxyguanine, B. 4349 
     Sodium hydride (60% in oil; 416 mg, 10.4 mmol) was added to a stirred solution of 4-bromothenyl alcohol (2.32 g, 12 mmol) in DMSO (5 ml). After 30 min, 6-chloro-2,4-diaminopyrimidine (1.45 g, 10 mmol) was added and the solution heated for 2 h at 80° C. Solvent was removed at 45° C.-50° C./0.5 mm and the oily residue triturated with water, yielding O6-(4-bromothenyl)-2,4-diamino-6-hydroxypyrimidine (2.83 g, 94%). 
     To a mixture of this diamine (1.8 g , 6 mmol) in acetic acid (34 ml) and water (68 ml) was added over 20 min a solution of NaNO 2  (0.6 g, 8.7 mmol) in water (24 ml). The purple 5-nitroso derivative (1.6 g, 81%) was filtered off and washed with water. 
     The 5-nitrosopyrimidine (330 mg, 1 mmol) in DMF 10 ml) was vigorously stirred at 55° C. with sodium hydrosulphite (609 mg, 3.5 mmol) and treated dropwise over 12 min with water (10 ml). Stirring was continued for 15 min longer and the solvent evaporated in vacuo. The residue was suspended in water (6 ml), the pH adjusted to 9 with ammonium hydroxide, and the product extracted with ethyl acetate. Drying and evaporation yielded O 6  -(4-bromothenyl)-2,4,5-triamino-6-hydroxypyrimidine (267 mg, 85%) as a yellow solid. 
     The triamine (250 mg, 0.79 mmol) in DMF (1 ml) was treated with 1,1&#39;-carbonyldiimidazole (162 mg, 1 mmol) under argon and the solution left for 24 h. Dilution with water yielded the product B. 4349 (226 mg, single spot on t.l.c.), which was dissolved in 2 M NaOH (30 ml), clarified by filtration, and reprecipitated by acetic acid, Recrystallisation yielded 138 mg (56%). 
     Type 2A. 
     O 6  -(4-Chlorothenyl)-8-azaguanine, B. 4314 
     O 6  -(4-Chlorothenyl)-2,4-diamino-5-nitroso-6-hydroxypyrimidine (286 mg, 1 mmol) was reduced by sodium hydrosulphite as a Type 1E and the triamine obtained dissolved in acetic acid (3 ml) and water (15 ml) at 0° C. NaNO 2  (75 mg, 1.1 mmol) in water (1.2 ml) was added dropwise and, after stirring for 1 hour the precipitate (150 mg) was collected and washed with water and recrystallised. 
     Type 2B. 
     O 6  -Thenyl-6-aza-7-deazaguanine, B. 4338 
     Sodium hydride (60% in oil; 80 mg, 2 mmol) was added to a solution of thenyl alcohol (342 mg, 3 mmol) in sulfolane (9 ml) with stirring and set aside for 30 minutes. 6-Chloro-8-aza-7-deazaguanine (170 mg, 1 mmol) in sulfolane (5 ml) was added and the reaction mixture heated at 65° C. for 2 hours. The mixture was then cooled and added to a solution of acetic acid (0.12 ml) in ether (100 ml). After 1 hour the sodium chloride was filtered off and the ether evaporated. The sulfolane was removed under reduced pressure (90° C. at 0.5 mmHg) and the residue washed with water and extracted with ethanol, yielding B. 4338 (168 mg, 68%) 
     O 6  -(4-chlorobenzyl)-8-aza-7-deazaguanine, B. 4339 
     DABCO (278 mg, 2.48 mmol) was added to a solution of 6-chloro-8-aza-7-deazaguanine (210 mg, 1.24 mmol) in DMF (3 ml) and the mixture stirred at room temperature for 1 hour. The precipitate of quaternary salt (260 mg, 75%) was removed by filtration and washed with acetone. Sodium hydride (60% in oil; 52 mg, 1.3 mmol) was added to a stirred solution of 4-chlorobenzyl alcohol (278 mg,1.95 mmol) in DMSO (2 ml) and the mixture stirred for 30 minutes. The quaternary salt (180 mg, 0.65 mmol) was added and after stirring at room temperature for 6 hours, the insoluble material was filtered off and treated with water (30 ml). The product B. 4339 (162 mg, 92%) was filtered off and dried. 
     Type 3A. 
     O 6  -(4-fluorobenzyl)-8-oxaguanine, B. 4272 
     O 6  -(4fluorobenzyl)-2,4diamino5-nitroso-hydroxypyrimidine (263 mg.1 mmol), prepared as in type IE, was suspended in acetic acid (4 ml). Lead tetraacetate (85%, 57 mg, 1.1 mmol) was added in portions with stirring over 10 minutes under nitrogen. After 1.5 hours the product (191 mg) was collected and dried. Recrystallisation from acetone yielded pure B. 4272. 
     Type 3B. 
     O 6  -(4-Bromothenyl)-8-Thiaguanine, B. 4351 
     A solution of O 6  -(4-bromothenyl)-2,4,5-triamino-6-hydroxypyrimidine (474 mg, 1.5 mmol), as prepared in Type 1E, and N-tosylthionylimine (652 mg, 3 mmol) in dry pyridine (15 ml) was stirred, under a nitrogen atmosphere, for 2h. The pyridine was removed in vacuo and successive amounts of EtOH were added and removed until a yellow solid was obtained. Crystallisation from methanol gave B 4351 (212 mg). 
     Type 3C. 
     O 4  -(4-Bromothenyl)pterin, B. 4288 
     A solution of glyoxal trimer (84 mg, 1.2 mmol) and sodium metabisulphite (228 mg, 1.2 mmol) in water (4 ml) at 80° C. was added in one portion to a refluxing solution of O 6  -(4-bromothenyl)-2,4,5-triamino-6-hydroxypyrimidine (316 mg, 1 mmol), prepared as in type 1E. The mixture was allowed to reach room temperature and the pH adjusted to 9. The solid (213 mg) was collected, dried and recrystallised from methanol to give B. 4288 (112 mg, 33%). 
     Type 4A. 
     O 6  -(4-Chlorothenyl)-2,4-diamino-6-hydroxypyrimidine, B.4302 
     Sodium hydride (60% in oil; 624 mg, 15.6 mmol) was added to a stirred solution of 4-chlorothenyl alcohol (2.7 g, 18 mmol) in DMSO (7.5 ml). After 30 min, 6-chloro-2,4-diaminopyrimidine (2.17 g, 15 mmol) was added and the solution heated for 2 h at 80° C. The solvent was removed in vacuo and the oily residue was triturated with water, yielding B.4302 (3.6 g). 
     Type 4B. 
     O 6  -(4-Chlorothenyl)-2,4-diamino-6-hydroxy-5-nitrosopyrimidine, B.4311 
     To a stirred solution of O 6  -(4-chlorothenyl)-2,4-diamino-6-hydroxyprimidine (257 mg, 1 mmol), prepared as Type 4A, in acetic acid (5.4 ml) and water (12.6 ml), was added a solution of NaNO 2  (100 mg, 1.45 mmol) in water (4 ml). The purple precipitate of B. 4311 (240 mg , single spot on t.l.c.) was collected and dried. 
     Type 4C. 
     O 6  -(4-Piperonyl)-2,4-diamino-6-hydroxy-5-nitropyrimidine, B.4308 
     Sodium hydride (60% in oil; 440 mg , 11 mmol) was added to a stirred solution of piperonyl alcohol (3.1 g, 20 mmol) in DMSO (5 ml). After 30 min, 2,4-diamino-6-chloro-5-nitropyrimidine (1.9 g, 10 mmol) was added and the mixture was stirred under argon for 3.5 h. Acetic acid (1 ml) in ether (300 ml) was added to the cooled mixture. Trituration with ether gave an oily solid (2.0 g) which was washed with water and dried. Recrystallisation from DMF gave B. 4308. 
     Type 5. 
     S 6  -(4-Bromothenyl)-6-thioguanine, B.4352 
     Sodium hydride (60% in oil; 44 mg , 1.1 mmol) was added to a solution of 4-bromothenyl mercaptan (418 mg, 2 mmol) in DMSO (0.5 ml). After 30 min, 2-amino-N,N,N-trimethyl-1H-purin-6-aminium chloride (228 mg, 1 mmol) was added and stirring continued 1 h. Acetic acid (0.12 ml) and ether (30 ml) were added and after decantation and trituration with fresh ether, B.4352 (38 mg, 11%) was filtered off. 
     
                                           TABLE Ia__________________________________________________________________________                       M.p.       O.sup.6 -Substituent              Yield                 Solvent for                       (decomp.)     Molecular  AnalysisCompound, Test No.       RCH.sub.2              %  Recrystn.                       (° C.)                            Formula  Weight     C  H   N__________________________________________________________________________Type 1A. HypoxoathinesB. 4293     furfuryl              60 MeOH  154  C.sub.10 H.sub.8 N.sub.4 O.sub.2                                       216B. 4291     theonly              66 MeOH  168  C.sub.10 H.sub.8 N.sub.4 OS                                       232  Found                                                51.85                                                   3.43                                                       24.12                                            Req.                                                51.71                                                   3.47                                                       24.12B. 4292     4-bromothenyl              69 MeOH  170  C.sub.10 H.sub.7 BrN.sub.4 OS                                       311  Found                                                38.33                                                   2.18                                                       17.66                                            Req 38.6                                                   2.26                                                       18.001B. 2-MethylhypoxanthinesB. 4347     benzyl 43 MeCN  191-193.sup.a                            C.sub.13 H.sub.12 N.sub.4 O                                       240  Found                                                65.05                                                   4.91                                                       23.30                                            Req 64.99                                                   5.03                                                       23.32B. 435C     thenyl 35 MeCN  176-178.sup.a                            C.sub.11 H.sub.10 N.sub.4 OS                                       325  Found                                                53.63                                                   3.90                                                       22.67                                            Req 53.64                                                   4.09                                                       22.751C. 2-FluorohypoxanthinesB. 4353     4-bromothenyl              55 Column                       142  C.sub.10 H.sub.6 BrFN.sub.4 OS                                       3291D. 9-(2-Hydroxyethoxy-methyl)guaniaesB. 4334     benzyl 45 i-PrOH                       150-152.sup.a                            C.sub.15 H.sub.17 N.sub.5 O.sub.3                                       315  Found                                                57.19                                                   5.59                                                       21.93                                            Req 57.13                                                   5.43                                                       22.21B. 4335     4-bromothenyl              42 i-PrOH                       156-158.sup.a                            C.sub.13 H.sub.14 BrN.sub.5 O.sub.3                                       40C  Found                                                39.16                                                   3.68                                                       17.20                                            Req 39.01                                                   3.53                                                       17.501E. 8-HydroxyguanninesB. 4349     4-bromothenyl              56 Aq. EtOH                       &gt;230 C.sub.10 H.sub.6 BrN.sub.5 O.sub.2                            S.1/2H.sub.2 O                                       351  Found                                                34.53                                                   2.48                                                       19.50                                            Req.                                                34.20                                                   2.58                                                       19.94Type 2A. 8-AragucaninesB. 4270     4-fluorobenzyl              40 Aq. MeOH                       &gt;280 C.sub.11 H.sub.9 FN.sub.6 O                                       260  Found                                                51.50                                                   3.85                                                       29.44                                            Req.                                                50.77                                                   3.49                                                       32.30B. 4314     4-chlorothenyl              26 Aq. MeOH                       &gt;200 C.sub.9 H.sub.7 ClN.sub.6 OS                                       282.7                                            Found                                                38.86                                                   2.61                                                       28.61                                            Req.                                                38.24                                                   2.50                                                       29.73B. 4289     4-bromothenyl              12 MeCN  &gt;190 C.sub.9 H.sub.7 BrN.sub.6 OS                                       327  Found                                                35.91                                                   2.78                                                       24.602B. 8-Aza-7-dezazguoninesB. 4310     benzyl    MeOH  160  C.sub.12 H.sub.11 N.sub.5 O.H.sub.2                                       259  Found                                                55.53                                                   4.9 26.41                            1/2H.sub.2 O.1/4EtOH                                            Req.                                                55.59                                                   5.01                                                       27.02B. 4340     4-fluorobenzyl              65 EtOH  188  C.sub.12 H.sub.10 FN.sub.5 O.1/4H.sub.2                            O          263.7                                            Found                                                53.82                                                   3.76                                                       26.97                            1/2H.sub.2 O.1/4EtOH                                            Req.                                                54.6                                                   4.0 26.55B. 4339     4-chlorobenzyl              92 EtOH  242-244.sup.a                            C.sub.12 H.sub.10 ClN.sub.5 O.                                       296  Found                                                51.15                                                   3.89                                                       23.43                            1/2H.sub.2 O.1/4EtOH                                            Req.                                                50.7                                                   4.25                                                       23.64B. 4343     piperonyl              50 EtOH  186B. 4348     furfuryl  EtOH  150.sup.a                            C.sub.13 N.sub.18 N.sub.5 O.sub.3                                       285  Found                                                54.52                                                   3.82                                                       24.50                                            Req.                                                54.7                                                   3.88                                                       24.55B. 4338     thenyl 68 EtOH  180  C.sub.10 H.sub.9 N.sub.5 O.sub.2.1/4H.sub                            .2 O       235.7                                            Found                                                50.96                                                   3.87                                                       29.54                                            Req.                                                50.96                                                   4.06                                                       29.71B. 4337     4-bromothenyl              79 EtOH  180  C.sub.10 H.sub.9 N.sub.5 OS                                       247  Found                                                47.58                                                   3.54                                                       27.41                                            Req.                                                47.7                                                   3.8 27.8                            C.sub.10 H.sub.8 BrN.sub.5 OS                                       326  Found                                                37.08                                                   2.51                                                       21.31                                            Req.                                                36.8                                                   2.5 21.5Type 3A. 8-OxaguaninesB. 4272     4-fluorobenzyl              41 Acetone                       223-224                            C.sub.11 H.sub.8 FN.sub.5 O.sub.2                                       261  Found                                                50.89                                                   3.08                                                       26.65                                            Req.                                                50.58                                                   3.09                                                       26.81B. 4285     4-chlorobenzyl              63 Acetone                       219-220                            C.sub.11 H.sub.8 ClN.sub.5 O.sub.2                                       277.7                                            Found                                                47.59                                                   2.88                                                       25.25                                            Req.                                                47.58                                                   2.90                                                       25.22B. 4299     4-chlorothenyl              55 Acetone                       164-165                            C.sub.9 H.sub.6 ClN.sub.5 O.sub.2                                       283.7                                            Found                                                37.68                                                   2.15                                                       24.43                                            Req.                                                38.10                                                   2.19                                                       24.69B. 4287     4-bromothenyl              61 Acetone                       170-172                            C.sub.9 H.sub.6 BrN.sub.5 O.sub.2                                       328  Found                                                33.30                                                   1.85                                                       21.37                                            Req.                                                32.94                                                   1.84                                                       21.343B. 8-ThlaguaninesB. 4296     benzyl 39 EtOH       C.sub.11 H.sub.9 N.sub.5 OS                                       259B. 4286     4-fluorobenzyl              11 PLC        C.sub.11 H.sub.8 FN.sub.5 OS                                       277B. 4315     4-chlorothenyl              13 MeOH       C.sub.9 H.sub.6 ClN.sub.5 OS.sub.2                                       299.8                                            Found                                                36.27                                                   2.04                                                       23.07                                            Req.                                                36.06                                                   2.02                                                       23.36B. 4351     4-bromothenyl              41 MeOH  156-160                            C.sub.9 H.sub.6 BrN.sub.5 OS.sub.2                                       344  Found                                                31.49                                                   1.60                                                       20.11                                            Req.                                                31.41                                                   1.76                                                       20.353C. Pterins (O.sup.4 -substituent)B. 4290     4-flurobenzyl              55 MeOH  &gt;210 C.sub.13 H.sub.10 FN.sub.5 O                                       271  Found                                                57.87                                                   3.88                                                       25.65                                            Req.                                                57.56                                                   3.72                                                       25.82B. 4316     4-chlorothenyl              41 MeOH  &gt;170 C.sub.11 H.sub.8 ClN.sub.5 OS                                       293.7                                            Found                                                44.93                                                   2.84                                                       23.72                                            Req.                                                44.98                                                   2.75                                                       23.84B. 4288     4-bromothenyl              63 MeOH  178-179                            C.sub.11 H.sub.8 BrN.sub.5 OS                                       338  Found                                                39.34                                                   3.13                                                       20.25                                            Req.                                                39.07                                                   2.38                                                       20.71Type 4A. 2,4-diamino-6-hydroxypyrimidinesB. 4305     4-fluorobenzyl              98 C.sub.6 H.sub.6 /Petrol                       133-134                            C.sub.11 H.sub.13 FN.sub.4 O                                       234  Found                                                56.20                                                   4.79                                                       23.66                                            Req.                                                56.40                                                   4.73                                                       23.92B. 4304     4-chlorobenzyl              31 C.sub.6 H.sub.6                       122-123                            C.sub.11 H.sub.13 ClN.sub.4 O                                       250.7                                            Found                                                52.43                                                   4.56                                                       22.47                                            Req.                                                52.70                                                   4.42                                                       22.35B. 4303     piperonyl              79 MeCN  168-171                            C.sub.12 H.sub.12 N.sub.4 O.sub.3                                       260  Found                                                55.31                                                   4.64                                                       21.38                                            Req.                                                55.38                                                   4.65                                                       21.52B. 4307     thenyl 97 MePh  100  C.sub.9 H.sub.10 N.sub.4 OS                                       222  Found                                                48.83                                                   4.58                                                       25.25                                            Req.                                                48.63                                                   4.54                                                       25.21B. 4302     4-chlorothenyl              45 MePh  129-130                            C.sub.9 H.sub.9 ClN.sub.4 OS                                       256.7                                            Found                                                42.40                                                   3.68                                                       22.00                                            Req.                                                42.11                                                   3.53                                                       21.834B. 2,4-Diamino-6-hydroxy-5-nitrosopyrimidinesB. 4301     4-fluorobenzyl              76 MeOH  &gt;250 C.sub.11 H.sub.10 FN.sub.5 O.sub.2                                       263  Found                                                49.60                                                   3.90                                                       26.29                                            Req.                                                50.19                                                   3.83                                                       26.61B. 4311     4-chlorothenyl              84 Acetone                       &gt;190 C.sub.9 H.sub.8 ClN.sub.5 O.sub.2                                       285.7                                            Found                                                37.54                                                   2.79                                                       24.22                                            Req.                                                37.84                                                   2.82                                                       24.51B. 4312     4-bromothenyl              62 Acetone                       200-201                            C.sub.9 H.sub.3 BrN.sub.3 O.sub.2                                       330  Found                                                32.87                                                   2.38                                                       20.95                                            Req.                                                32.74                                                   2.44                                                       21.214C. 2,4-Diamino-6-hydroxy-5-nitropyrlaudinesB. 4308     piperonyl              67 DMF   &gt;175 C.sub.12 H.sub.11 N.sub.5 O.sub.5                                       365  Found                                                47.44                                                   4.07                                                       22.83                                            Req.                                                47.22                                                   3.63                                                       22.94B. 4306     thenyl 34 MeOH  159-160                            C.sub.9 H.sub.9 N.sub.5 O.sub.2 S                                       267  Found                                                40.99                                                   3.71                                                       25.99                                            Req.                                                40.44                                                   3.39                                                       26.21__________________________________________________________________________ .sup.a Without decomposition 
    
     
                                           TABLE Ib__________________________________________________________________________                    λ.sub.min (MeOH)Compound Type, Test No.          O.sup.6 -Substituent RCH.sub.2                    (nm)  δ.sub.H /ppm from TMS,                          (CD.sub.3).sub.2 SO, /J(Hz)__________________________________________________________________________Type 1A. HypoxanthinesB. 4293        furfuryl  252   5.60(s), 6.53(dd, 3.1, 1.9), 6.69(d, 3.1),                          7.76(dd, 1.9, 0.9) 8.39(s), 8.55(s)B. 4291        thenyl    240   5.63(s), 7.08(dd, 5.1, 3.4), 7.35(d, 3.4),                          7.6(d, 5.1), 8.39(s), 8.51(s)B. 4292        4-bromothenyl                    251   5.80(s), 7.38(d, 1.3), 7.73(d, 1.3),                          8.42(s), 8.58(s)Type 1B. 2-MethyltypoxanthinesB. 4347        benzyl    256   2.61(s), 5.60(s), 7.50(m), 8.32(s)B. 4350        thenyl    240   2.63(s), 5.77(s), 7.05(dd, 5.1, 2.4,                          7.33(d), 2.4), 7.58(dd, 5.1, 1.0)                          8.25(s),                          13.22(s)Type 1C. 2-FluorohypoxanthinesB. 4353        4-bromothenyl                    233, 255                          5.77(s), 7.4(d, 1.5), 7.77(d, 1.5),                          8.45(s), 13.64(bs).Type 1D. 9-(2-Hydroxyethoxymethyl,guaninesB. 4334        benzyl    247, 283                          3.48(m), 4.70(s), 5.45(s), 6.59(s),                          7.45(m), 8.03(s),B. 4335        4-bromothenyl                    245, 284                          3.49(m), 4.71(s), 5.45(s), 5.56(s),                          6.65(s), 7.30(d, 1.5) 7.72(d, 1.5)                          8.04(s)Type 1E. 8-HydroxyguaninesB. 4349        4-bromothenyl                    239, 293                          5.54(s), 6.24(s), 7.33(d, 1.4) 7.70(d,                          1.4), 10.49(s) 11.12(s)Type 2A. 8-AzaguaninesB. 4270        4-fluorobenzyl                    288   5.57(s), 7.04(s), 7.28(m), 7.65(m),                          15.38(s).B. 4314        4-chlorothenyl                    288   5.71(s), 7.13(s), 7.41(d, 1.5), 7.66(d,                          1.5), 15.42(s).B. 4289        4-bromothenyl                    287   5.73(s), 7.12(s), 7.43(d, 1.5), 7.76(d,                          1.5), 15.39(s).Type 2B. 8-Aza-7-deazaguaninesB. 4310        benzyl    277   5.50(s), 6.68(s), 7.74(m), 7.82(s),                          12.87(bs)B. 4340        4-fluorobenzyl                    278   5.49(s), 6.70(s), 7.20(m), 7.61(m),                          7.82(s), 12.88(bs)B. 4339        4-chlorobenzyl                    276   5.50(s), 6.69(s), 7.49(d, 8.4), 7.56(d,                          8.4), 7,83(s) 12.90(s).B. 4343        piperonyl 282   5.39(s), 6.05(s), 6.69(s), 6.94(d, 7.9)                          7.04(dd, 7.9, 1.5), 7.14(d, 1.5), 7.80(                          12.86(bs).B. 4348        furfuryl  277   5.46(s), 6.52(s), 6.70(s), 6.71(s),                          7.73(s), 7.79(s), 12.85(bs).B. 4338        thenyl    278   5.69(s), 6.73(s), 7.07(d, 3.5), 7.35(s),                          7.60(d, 1.1), 7.79(s), 12.90(bs).B. 4337        4-bromothenyl                    278   5.65(s), 6.76(s), 7.38(s), 7.72(d, 1.3),                          7.81(s), 12.91(bs).Type 3A. 8-OxaguaninesB. 4272        4-fluorobenzyl                    257, 341                          5.62(s), 7.30(t, 9.1), 7.68(m), 7.91(s),                          7.97(s).B. 4285        4-chlorobenzyl                    256, 340                          5.63(s), 7.53(d, 8.3), 7.65(d, 8.3),                          7.90(s), 7.97(s).B. 4299        4-chlorothenyl                    252, 343                          5.78(s), 7.46(d, 1.6), 7.72(d, 1.6),                          7.95(s), 8.01(s).B. 4287        4-bromothenyl                    253, 343                          5.79(s), 7.49(d, 1.6), 7.81(d, 1.6),                          7,95(s), 8.01(s).Type 3B. 8-ThiaguaninesB. 4296        benzyl    227, 361B. 4286        4-fluorobenzyl                    235, 361                          5.59(s), 7.29(t 8.9), 7.51(bs), 7.67(m)B. 4315        4-chlorothenyl                    228, 360                          5.75(s), 7.44(d, 1.6), 7.55(bs), 7.69(d,                          1.6).B. 4351        4-bromothenyl                    228, 361                          5.78(s), 7.45(d, 1.6), 7.46(bs), 7.75(d.                          1.6)Type 3C. Pterins (O.sup.4 -substituent)B. 4290        4-fluorobenzyl                    232, 264(sh),                          5.56(s), 7.29(t, 8.85), 7.44(bs), 7.66(m),                          8.45(d, 1.8), 8.82(d, 1.8).                    362B. 4316        4-chlorothenyl                    232, 364                          5.71(s), 7.41(d, 1.6), 7.47(bs), 7.67(d,                          1.6), 8.46(d, 2.0), 8.83(d, 2.0)B. 4288        4-bromothenyl                    231, 364                          5.73(s), 7.44(d, 1.6), 7.50(bs), 7.77(d,                          1.6) 8.46(d, 2) 8.83(d, 2).Type 4A. 2,4-diamino-6-hydroxy-pyrimidinesB. 4305        4-fluorobenzyl  5.10(s), 5.19(s), 5.96(s), 6.10(s),                          7.19(t, 8.8), 7.44(dd, 8.8, 5.8).B. 4304        4-chlorobenzyl  5.11(s), 5.22(s), 5.96(s), 6.10(s),                          7.44(s).B. 4303        piperonyl       5.09(s), 5.12(s), 5.97(s), 6.03(s),                          6.07(s), 6.91(d, 1.1), 7.00(s).B. 4307        thenyl          5.08(s), 5.40(s), 6.00(s), 6.10(s),                          7.03(dd, 3.1, 3.5)7.20(dd, 8.1, 1.1),                          7.54                          (dd, 3.5, 1.1).B. 4302        4-chlorothenyl  5.08(s), 5.35(s), 6.03(s), 6.3(s),                          7.19(s), 7.55(d, 1.6).Type 4B. 2,4-Diamino-6-hydroxy-5-nitrosopyrimidinesB. 4301        4-fluorobenzyl                    336   5.59(s), 7.26(m), 7.65(m), 7.80(bs),                          7.86(bs), 8.00(bs), 10.05(bs).B. 4311        4-chlorothenyl                    335   5.73(s), 7.40(d, 1.6), 7.66(d, 1.6),                          7.94(s), 7.98(d, 2.7), 8.10(d, 4.2) 10.03                          (d, 4.2).B. 4312        4-bromothenyl                    335   5.75(s), 7.42(d, 1.4), 7.75(d, 1.4),                          7.93(s), 7.98(s), 8.12(d, 4.0), 10.04                          (d, 4.0)Type 4C. 2,4-diamino-6-hydroxy-5-nitropyrimidinesB. 4308        piperonyl 288, 330                          5.33(s), 6.05(s), 6.95(d, 8.0), 7.00(dd,                          8.0, 1.4), 7.10(d, 1.4), 7.26(bs), 7.3                          7.96(bs).B. 4306        thenyl    234, 329                          5.59(s), 7.03(dd, 5.1, 3.5), 7.28(d, 3.5),                          7.32(bs), 7.56(d, 5.1), 7.94(bs).__________________________________________________________________________ 
    
     
                       TABLE 2______________________________________INACTIVATOR TYPE            I.sub.50 (μM)______________________________________1A  B.4291                      1.9    0.sup.6 (thenyl)-hypoxanthine    B.4293                      28    0.sup.6 -(furfuryl)-hypoxanthine    B.4292                      0.3    0.sup.6 -(4-bromothenyl)-hypoxanthine    0.sup.6 -(benzyl)-hypoxanthine.sup.b                           851B  B.4347                      75    0.sup.6 -(benzyl)-2-methylhypoxanthine    B.4350                      14    0.sup.6 -(thenyl)-2-methylhypoxanthine1C  B.4353    0.sup.6 (4 bromothenyl)-2-fluoro,hypoxanthine    0.sup.6 -(benzyl)-2-fluorohypoxanthine.sup.a                           481D  B.4334                      8    0.sup.6 -(benzyl)-9-(2-hydroxyethoxymethyl)guanine    B.4335                      0.33    0.sup.6 -(4 bromothenyl)-9-(2-hydroxyethoxymethyl)guanine1E  B.4349                      0.018    0.sup.6 -(4-bromothenyl)-8-hydroxyguanine    0.sup.6 -(benzyl)-8-hydroxyguanine.sup.a                           0.032A  B.4270                      0.08    0.sup.6 -(4-fluorobenzyl)-8-azaguanine    B.4314                      0.011    0.sup.6 -(4-chlorothenyl)-8-azaguanine    B.4289                      0.045    0.sup.6 -(4-bromothenyl)-8-azaguanine    0.sup.6 -(benzyl)-8-azaguanine.sup.a                           0.072B  B.4310                      0.0093    0.sup.6 -(benzyl)-8-aza-7-deazaguanine    B.4340                      0.018    0.sup.6 -(4-fluorobenzyl)-8-aza-7-deazaguanine    B.4339                      0.02    0.sup.6 -(4-chlorobenzyl)-8-aza-7-deazaguanine    B.4343                      0.0065    0.sup.6 -(piperonyl)-8-aza-7-deazaguanine    B.4348                      0.036    0.sup.6 -(furfuryl)-8-aza-7-deazaguanine    B.4338                      0.01    0.sup.6 -(thenyl)-8-aza-7-deazaguanine    B.4337                      0.007    0.sup.6 -(4-bromothenyl)-8-aza-7-deazaguanine3A  B.4272                      0.02    0.sup.6 -(4-fluorobenzyl)-8-oxaguanine    B.4285                      0.225    0.sup.6 -(4-chlorobenzyl) 8 oxaguanine    B.4299                      0.243    0.sup.6 (4-chlorothenyl)-8-oxaguanine    B.4287                      0.24    0.sup.6 -(-4-bromothenyl)-8-oxaguanine    B.4232                      0.25    0.sup.6 -(benzyl)-8-oxaguanine3B  B.4296                      0.02    0.sup.6 -(benzyl)-8-thiaguanine    B.4286                      0.03    0.sup.6 -(4-fluorobenzyl)-8-thiaguanine    B.4315                      0.006    0.sup.6 -(4-chlorothenyl)-8-thiaguanine    B.4351                      0.0028    0.sup.6 -(4-bromothenyl)-8-thiaguanine3C  B.4290                      0.088    0.sup.4 -(4-fluorobenzyl)-pterin    B.4316                      0.025    0.sup.4 -(4-chlorothenyl) pterin    B.4288                      0.025    0.sup.4 -(4-bromothenyl)-pterin4A  B.4305                      4.0    2,4-diamino-6-(4-fluorobenzyloxy)pyrimidine    B.4304                      5.0    2,4-diamino-6-(4-chlorobenzyloxy)pyrimidine    B.4303                      0.8    2,4-diamino-6-(3,4-piperonyloxy)pyrimidine    B.4307                      0.4    2,4-diamino-6-(thenyloxy)pyrimidine    B.4302                      0.17    2,4-diamino-6-(4-chlorothenyloxy)pyrimidine    2,4-diamino-6-(benzyloxy)pyrimidine.sup.a                           154B  B.4301                      0.0175    2,4-diamino-6-(4-fluorobenzyloxy)-5-nitrosopyrimidine    B.4311                      0.009    2,4-diamino-(4-chlorothenyloxy)-5-nitrosopyrimidine    B.4312                      0.045    2,4-diamino-6-(4-bromothenyloxy)-5-nitrosopyrimidine    2,4-diamino 6-(benzyloxy)-5-nitrosopyrimidine.sup.a                           0.064C  B.4306                      2.3    2,4-diamino-6-(thenyloxy)-5-nitropyrimidine    B.4308                      0.5    2,4-diamino-6-piperonyloxy-5-nitropyrimidine    2,4-diamino-6-benzyloxy-5-nitropyrimidine.sup.a                           0.06______________________________________ .sup.a Data taken from Chae et al, J. Med. Chem. 1995, 38, 359-365 .sup.b Data taken from Moschel et al., J. Med. Chem. 1992, 35, 4486-4491. 
    
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