SOLID SUPPORT SYNTHESIS OF 2-OXOPIPERAZINES

Abstract: The subject invention involves processes for making 2-oxopiperazine and homologous compounds using a solid support resin by (a) removing the protecting group from an N-protected amino acid ester of the resin (if present), (b) reacting the resulting unprotected resin ester with a N-protected alpha -amino aldehyde, (c) optionally modifying the resulting intermediate by substituting a non-hydrogen moiety on the N from the amino acid, (d) removing the remaining N-protecting group from the N from the amino aldehyde, and (e) cleaving/cyclizing the product from the resin.

Description: Solid Support Synthesis of 2-Oxopiperazines TECHNICAL FIELD The subject invention relates to methods for synthesizing 2-oxopiperazine and homologous compounds, including libraries of such compounds, using a solid- support resin to facilitate purification of intermediates. BACKGROUND OF THE INVENTION Many of the first combinatorial libraries were developed around the well documented solid supported syntheses of peptides and transformations of amino acid resin esters. As a consequence, several syntheses of hydantoins and diketopiperazines have been reported. See a) Gordon, D. W.; Steele, J.; Bioorg. Med. Chem. Lett., vol. 5 (1995), p. 47; b) Kowalski, J.; Lipton, M. A.; Tetrahedron Lett., vol. 37 (1996), p. 5839; c) Scott, B. O.; Siegmund, A. C; Marlowe, C. K.; Pei, Y.; Spear, K. L.; Mol. Diversity, vol. 1 (1995), p. 125; d) Goodfellow, V. S.; Laudeman, C. P.; Gerrity, J. I.; Burkard, M.; Strobel, E.; Zuzack, J. S.; McLeod, D. A.; Mol. Diversity, vol. 2 (1 96), p. 97. The latter class of compounds possesses a rigid scaffold and has proven to be an effective screening tool, but also has several limitations, solubility and metabolic stability. There are only a few reports on the synthesis of piperazines and 2-oxopiperazines on solid support. See a) Goff, D. A.; Zuckremann, R. N.; Tetrahedron Lett, vol. 37 (1996), p. 6247; b) Dankwardt, S. M.; Sherry, R. N.; Krstenansky, J. Tetrahedron Lett. vol. 36 (1995), p. 4923. SUMMARY OF THE INVENTION The subject invention involves processes for making 2-oxopiperazine compounds: HN ■v ' using a solid-support resin, comprising the following steps: (a) starting with a N-protected α-amino acid ester of a solid-support resin: R 1 (1) removing the N-protecting group from (1), and reacting the unprotected ester with a N-protected α-amino aldehyde: NHBI OHC R 2 , (2) to provide: ; (1) (b) optionally modifying 3 by substituting a non-hydrogen moiety R^ for the hydrogen on the N from I to provide: O R 1 BIHN R 2 ; (4) (c) removing the N-protecting group from 4, and cyclizing 5 from the resin. The subject invention also includes the above processes where the α-amino ester (V) is replaced by a β-amino ester (or other homologous ester) such that the final products are the homologous 7-member (or larger) ring compounds. DETAILED DESCRIPTION OF THE INVENTION As used herein unless specified otherwise, "alkyl" means a hydrocarbon chain which is branched, linear or cyclic, saturated or unsaturated (but not aromatic), substituted or unsubstituted. The term "alkyl" may be used alone or as part of another word where it may be shortened to "alk" (e.g., in alkoxy, alkylacyl). Preferred linear alkyl have from one to about twenty carbon atoms, more preferably from one to about six carbon atoms, more preferably still from one to about four carbon atoms; most preferred are methyl or ethyl. Preferred cyclic and branched alkyl have from three to about twenty carbon atoms, more preferably from three to about six carbon atoms. Preferred cyclic alkyl have one hydrocarbon ring, but may have two, three, or more, fused hydrocarbon rings. Preferred alkyl are unsaturated with from one to about three double or triple bonds; preferably they are mono- 3 unsaturated with one double bond; more preferred alkyl are saturated. Preferred substituents of alkyl include alkyl, aryl, aryloxy, alkoxy, alkyl or aryl ester. More preferred alkyl are unsubstituted. As used herein unless specified otherwise, "aryl" means an aromatic hydrocarbon ring which is substituted or unsubstituted. The term "aryl" may be used alone or as part of another word (e.g., in aryloxy, arylacyl). Preferred aryl have from six to about ten carbon atoms in the aromatic ring(s), and a total of from about six to about twenty, preferably to about twelve, carbon atoms. Preferred aryl is phenyl or naphthyl; most preferred is phenyl. Preferred substituents of aryl include alkyl, aryl, alkoxy, aryloxy, alkyl or aryl ester, halo, nitro, amino, cyano, acyl, alkyl- or arylacyl. More preferred aryl are unsubstituted. As used herein, "heteroatom" means a nitrogen, oxygen, or sulfur atom. As used herein unless specified otherwise, "heterocycle" means a cyclic alkyl with one or more heteroatoms in the hydrocarbon ring(s). Preferred heterocycles have from one to about six heteroatoms in the ring(s), more preferably one or two or three heteroatoms, most preferably one heteroatom. Preferred heterocycles have from three to about ten carbon plus heteroatoms in the ring(s), more preferably from three to about seven; and a total of from three to about twenty carbon plus heteroatoms, more preferably from three to about ten. Preferred heterocycles have one ring, but may have two, three, or more, fused rings. Heterocycles are unsubstituted or substituted. Preferred heterocycle substituents are the same as for alkyl. As used herein unless specified otherwise, "heteroaryl" means an aromatic hydrocarbon ring with one or more heteroatoms in the ring(s). Preferred heteroaryls have from one to about six heteroatoms in the ring(s), more preferably one or two or three heteroatoms, most preferably one heteroatom. Preferred heteroaryls have from five to about twelve carbon plus heteroatoms in the aromatic ring(s), more preferably from five to about nine; and a total of from five to about twenty carbon plus heteroatoms, more preferably from five to about ten. Preferred heteroaryls have one ring, but may have two or more fused rings, at least one of which contains at least one ring heteroatom. Heteroaryls are unsubstituted or substituted. Preferred heteroaryl substituents are the same as for aryl. The subject invention processes use solid-support resins capable of linking with the carboxy moiety of amino acids. Preferred resins for use in the subject processes have hydroxymethylene linking moieties. Particularly preferred are Merrifield or Wang resins such as polystyrene based resin Merrifield (100-200 mesh), 4 2%DVB - catalog number 01-64-0104, available from Calbiochem-Novabiochem Corp., San Diego, California, a hydroxymethylpolystyrene resin. N-protected amino acids can be readily esterified to the above-mentioned resins. Alternatively, such resins are commercially available with N-protected amino acids already esterified to the resin (e. g. Boc-Gly-Merrifield resin catalog number 04-12-2507, available from Calbiochem-Novabiochem Corp., San Diego, California). N-protecting groups on the above-mentioned amino acids are well known; they include t-butyloxycarbonyl (Boc) and 9-fluorenylmethoxycarbonyl (Fmoc); most preferred is Boc. In the structures depicted herein, "Bl" is used to indicate a N- protecting group . A subject invention process involves starting with a N-protected amino acid ester of a solid-support resin: O BIHN R (6) The N-protecting group is generally present on amino acid esters of resins because it is needed to properly esterify the amino acid onto the resin. The subject process first requires removing this N-protecting group; this can be accomplished using any known method. (If the N-protecting group is not present, this procedure can be skipped.) The resulting unprotected amino acid ester of a solid-support resin is reacted with a N-protected α-amino aldehyde: NHBI OHC A R 2 2 (2) to provide: BIHN-{ R 2 (7) This procedure is reductive amination of the unprotected amino acid ester of a solid-support resin with the N-protected α-amino aldehyde. Various conditions for reductive amination reactions are known and can be used in this step. The reaction is preferably carried out under acidic to neutral conditions in a mildly polar solvent. 5 In structures 6 and 7 above, R* can be any moiety that provides stable intermediates and final products for the subject processes. Preferred R include hydrogen, alkyl, aryl, heterocycle, heteroaryl, alkyl or aryl amine, alkyl or aryl ester; more preferred R^ are hydrogen and alkyl. In structures 2 and 7 above, R^ can be any moiety that provides stable intermediates and final products for the subject processes. Preferred R^ include hydrogen, alkyl, aryl, heterocycle, heteroaryl, alkyl or aryl amine, alkyl or aryl ester; more preferred R^ are hydrogen and alkyl. N-protected α-amino aldehydes are readily prepared from commercially available N-protected amino alcohols; a preferred method is oxoammonium oxidation. See Lenna, M. R.; Sowin, T. J.; Morton, H. E.; Tetrahedron Lett., vol. 33 (1992), p. 5029. In structures 6 and 7 above, n is an integer from 0 to about 5, preferably from 0 to about 3; more preferably n is 0 or 1, most preferably 0. The next step of a subject invention process is optional. It involves modifying 7 by substituting a non-hydrogen moiety R^ for the hydrogen on the nitrogen from 6 (the N bonded to the carbon to which R is also bonded) to provide: (8) R can be any moiety that provides stable intermediates and final products for the subject processes. Preferred R-* include hydrogen, alkyl, aryl, heterocycle, heteroaryl, alkyl or aryl amine, alkyl or aryl acyl, alkyl or aryl ester, alkyl or aryl sulfonyl; more preferred R^ include alkyl or aryl ester, alkyl or aryl sulfonyl. Examples of reactions for providing R^ in structure 8 include acetylation, sulfonylation, urea formation, reductive amination. The next step of a subject invention process involves removing the N- protecting group from 8 by any known method (similar to the analogous procedure above). The next step of a subject invention process involves cyclizing the product: (2) 6 from the resin. This cyclizing/cleavage from resin reaction is carried out in acidic conditions in a mildly polar solvent at an elevated temperature. Cleavage and cyclization is preferably achieved in a solution of acetic acid in 2-butanol. The cleavage and cyclization reaction is not highly dependent on the amino acid or amino aldehyde used. There is substantial difference between six and seven member ring formation, the latter being cleaved and cyclized much slower. The temperature required for substantially complete cleavage and cyclization is typically about 60-70°C. The subject invention processes are useful for making compounds individually or in libraries of separate or mixtures of compounds. The synthesis of libraries of compounds of structure 9 can readily be carried out using a multiple cell procedure, e.g., 96 plate format (e.g., Robbins Block), where different compounds having different combinations of Rl, R^ and R^ can be made in each cell simultaneously. Also, libraries of mixtures of compounds of structure 9 can be made by reacting reagents which are mixtues rather than single compounds. Both types of libraries are useful for rapid screening of numerous compounds for pharmacological and other activities. An exemplary process of the subject invention is depicted in the following scheme: 1. TFA, DCM 9 . R 0 2. 1% AcOH/DMF Q^W ' R NHBoc NaBH 3 CN ^ NH NHBoc BocHN R 2 OHC^TR 2 ^ O ^ O 3 TFA| DCM m γ R^ 1 , 2. 2M AcOH/2-BuOH RZ-'^NR BocHN N ^ R 2 4 5 The following example of the synthesis of 5a of the table below is typical. Boc-glycine Merrifield resin ester (75 mg, 1.00 mM/g loading, 0.075 mM) is suspended in dichloromethane (DCM) for 5 min. The solvent is filtered off. 25% trifluoroacetic acid (TFA) / DCM is added and the mixture is shaken at room temperature for 1 hour to remove the Boc protecting group. After this time, the resin is filtered, washed with a 10% solution of diisopropylethylamine in DCM, and then a 1% solution of acetic acid in dimethylformamide (DMF). The wet resin is suspended in a 1% solution of acetic acid in DMF and 4 eq (excess) of sodium cyanoborohydride (0.3 mM, 20 mg) is added to the 1% solution of acetic acid in DMF, followed by 2 eq of Boc-leucinal (0.15 mM, 32 mg). After 16-48 hours the reaction mixture is filtered, and the resin is washed with methanol, DMF and DCM. 25% TFA / DCM (ca. 5 mL) is added at room temperature and the resin is shaken for 1 hour to remove the Boc protecting group; then it is filtered and washed with DCM and methanol several times. A 2M solution of acetic acid in 2-butanol (ca. 10 mL) is added, and the reaction mixture is heated for 15 hours at 110°C, filtered and the resin washed three times with small amounts of DCM. Combined filtrates are evaporated and dried under vacuo to give crude product 5a (11.1 mg). Examples 5b - 5e of the table below are synthesized in a similar manner as 5a. Cyclization cleavage of the compound 5e requires longer time (72 hours). Starting Resin Amino Ester α - Amino Aldehyde 2-Oxopiperazine (5) O O O NHBoc HfΛ NHBoc A^NH 5a O O O H ' NHBoc NHBoc A ^ NH Ok O -ON COΝH 2 HN ,,^ CONH 2 NHBoc NH 5 C NHBoc O Ό Ph NHBoc HV HN' 'Ph NHBoc A ^ NH 5d -- NHBoc HV HN NHBoc <Λ -NH While particular embodiments of the subject invention have been described, it will be obvious to those skilled in the arts that various changes and modifications of the subject invention can be made without departing from the spirit and scope of the invention. It is intended to cover, in the appended claims, all such modifications that are within the scope of this invention.

Claims: WHAT IS CLAIMED IS: 1. A process for making compounds having the structure: (2) wherein, R , R^, and R^ are selected such that compounds 6, 2, 7, 8, and 9 are sufficiently stable to carry out the process, n is an integer from 0 to 5, and Bl is a N-protecting group, comprising the following steps: (a) from a N-protected amino acid ester of a solid-support resin: O O BIHN R (6) removing the N-protecting group Bl and substituting therefor a hydrogen to give an unprotected amino acid ester of a solid-support resin; or starting with such unprotected resin ester; (b) reacting the unprotected resin ester from step (a) with a N-protected α- amino aldehyde: NHBI OHC R 2 0) to provide: NH BIHN- * _ 2 , CD (b) optionally modifying 7 by substituting a non-hydrogen moiety R^ for the hydrogen on the N from 6 to provide: BIHN-{ \ R 2 , (8) (d) removing the N-protecting group from 8; and (e) cleaving and cyclizing 9 from the resin. 2. The process of Claim 1 wherein (a) R! is selected from hydrogen, alkyl, aryl, heterocycle, heteroaryl, alkyl or aryl amine, alkyl or aryl ester; (b) R2 is selected from hydrogen, alkyl, aryl, heterocycle, heteroaryl, alkyl or aryl amine, alkyl or aryl ester; and (c) R3 is selected from of hydrogen, alkyl, aryl, heterocycle, heteroaryl, alkyl or aryl amine, alkyl or aryl ester, alkyl or aryl acyl, alkyl or aryl sulfonyl. 3. The process of Claim 1 or 2 wherein n is 0 or 1. 4. The process of any of Claims 1-3 wherein step (e) is carried out in an acetic acid/2-butanol solution. 5. The process of any of Claims 1-4 wherein step (c) is carried out using a reaction procedure selected from acetylation, sulfonation, urea formation, reductive amination. 6. The process of any of Claims 1-5 wherein (a) n is 0 or 1 (b) R! is hydrogen or alkyl; (c) R2 is hydrogen or alkyl; (d) R3 is selected from hydrogen, alkly or aryl ester, and alkyl or aryl sulfonyl. 7. The process of any of Claims 1-6 wherein each N-protecting group is Boc or Fmoc, and steps (a) and (d) are carried out in a TFA/DCM solution. 10 8. The process of any of Claims 1-7 wherein the resin is hydroxymethylpolystyrene. 9. The process of any of Claims 1-8 wherein n is 0. 10. A library of compounds having structure: O ,2/\ • N. N R_3 c wherein the compounds are made using the process of any of Claims 1-9.

Inventors: GOLEBIOWSKI ADAM, KLOPFENSTEIN SEAN REES, GOLEBIOWSKI, ADAM, KLOPFENSTEIN, SEAN, REES
Applicants: GOLEBIOWSKI ADAM, KLOPFENSTEIN SEAN REES, PROCTER & GAMBLE, GOLEBIOWSKI, ADAM, KLOPFENSTEIN, SEAN, REES, THE PROCTER & GAMBLE COMPANY
Application year: 1999
Main classification: C07D241
IPC codes: C07D241, C07D243, C07D245