1.Preparation of N-acetyl, tert-butyl amide derivatives of the 20 natural amino acids.
Ekkati AR1, Campanali AA, Abouelatta AI, Shamoun M, Kalapugama S, Kelley M, Kodanko JJ. Amino Acids. 2010 Mar;38(3):747-51. doi: 10.1007/s00726-009-0279-y. Epub 2009 Mar 31.
N-Acetyl-AA(amino acid)-NHtBu derivatives of all 20 naturally occurring amino acids have been synthesized. Syntheses were performed via solution-phase methodology with yields that allow for access to gram quantities of substrates, in most cases. Syntheses include the coupling of a hindered amine, tert-butylamine, with each amino acid, either directly or in two steps using an activated ester isolated as an intermediate. The introduction of protecting groups was necessary in some cases. The development of synthetic sequences to access challenging substrates, such as the one derived from asparagine, are discussed.
2.Potential inhibitors of L-asparagine biosynthesis. 5. Electrophilic amide analogues of (S)-2,3-diaminopropionic acid.
Mokotoff M, Logue LW. J Med Chem. 1981 May;24(5):554-9.
Three electrophilic amide analogues of (S)-2,3-diaminopropionic acid (1, DAP) have been prepared as potential inhibitors of L-asparagine synthetase (ASase, from Novikoff hepatoma, EC 6.3.5.4). DAP was selectively blocked by the carbobenzoxy (Cbz) group to give 3-N-Cbz-DAP (2a). Esterification of 2a with isobutylene afforded tert-butyl 3-N-carbobenzoxy-(S)-2,3-diaminopropionate (3a), which was then blocked at the 2 position with the tert-butoxycarbonyl (Boc) group to give tert-butyl 2-[(S)-(tert-butoxycarbonyl)amino]-3-[(carbobenzoxy)amino]propionate (4). Selective cleavage of the Cbz group by H2/Pd gave the key intermediate tert-butyl 2-N-(tert-butoxycarbonyl)-(S)-2,3-diaminopropionate (5), which was acylated, via the N-hydroxysuccinimide esters, with bromoacetic acid, dichloroacetic acid, and fumaric acid monoethyl ester to give tert-butyl 2-[(S)-(tert-butoxycarbonyl)-amino]-3-(2-bromoacetamido)propionate (6a), tert-butyl 2-[(S)-(tert-butoxycarbonyl)amino]-3-(2,2-dichloroacetamido)propionate (6b), and tert-butyl 2-[(S)-(tert-butoxycarbonyl)amino]-3-(ethoxycarbonyl)acrylamido]-propionate (6c), respectively.
3.Potential inhibitors of L-asparagine biosynthesis. 4. Substituted sulfonamide and sulfonylhydrazide analogues of L-asparagine.
Brynes S, Burckart GJ, Mokotoff M. J Med Chem. 1978 Jan;21(1):45-9.
Several N-substituted sulfonamides and N'-substituted sulfonylhydrazides have been prepared as sulfur analogues of L-asparagine with the potential of acting as inhibitors of L-asparagine synthetase (ASase, from Novikoff hepatoma). L-Cysteine was converted in known steps to N-carboxy-3-(sulfonylchloro)-L-alanine dibenzyl ester (1). Condensation of 1 with O-benzylhydroxylamine, p-(fluorosulfonyl)benzylamine, or monoethyl fumarylhydrazide (9), followed by deblocking with HF, gave 3-(hydroxysulfamoyl)-L-alanine (3a), 3-[p-(fluorosulfonylbenzyl)]sulfamoyl-L-alanine (3c), and 3-sulfo-L-alanine S-[2-[(E)-3-(ethoxycarbonyl)acryloyl]hydrazide] (3e), respectively. Similarly, 1 with 2-chloroethylamine and deblocking with H2-Pd gave 3-[(2-chloroethyl)sulfamoyl]-L-alanine (3b). tert-Butyl carbazate was allowed to react with 1 and the tert-butyl group was removed with HCl. The resulting sulfonylhydrazide 7 was condensed with p-(fluorosulfonyl)benzoyl chloride and then deblocked with HF to give 3-sulfo-L-alanine S-[2-[P-(fluorosulfonyl)benzoyl]hydrazide] (3d).
4.Synthesis of glycopeptides and neoglycoproteins containing the fucosylated linkage region of N-glycoproteins.
Unverzagt C1, Kunz H. Bioorg Med Chem. 1994 Nov;2(11):1189-201.
N-Glycoproteins fucosylated in the core region occur in tumor membranes and virus envelopes. Partial structures of such N-glycoproteins containing fucosylated chitobiosyl asparagine conjugates were synthesized using the allyloxycarbonyl (Aloc) and the tert-butyl ester protecting groups in the peptide portion. As the alpha-fucosidic bond of the conjugates revealed to be very sensitive to acids when carrying ether-type protecting groups, a method for exchanging the protecting groups of the fucose portion of saccharides was developed. Conjugates containing O-acetyl protected fucose proved to be stable against acids used in glycopeptide syntheses. These methods were applied in the synthesis of a fucosyl chitobiose hexapeptide with the partial sequence of a leukemia virus envelope glycoprotein. The glycopeptide was coupled to bovine serum albumin yielding a neoglycoprotein which contains a glycoconjugate of exactly specified structure.
