Efficient Synthesis of Differentially Protected (S,S)-2,7- Diaminooctanedioic Acid, the Dicarba Analogue of Cystine
摘要:
Convenient preparative syntheses of differentially protected forms of (S,S)-2,7-diaminooctanedioic acid (2), suitable for application in peptide chemistry, are described. The key compound, the di-Cbz-protected phenacyl monoester 7a (Cbz = [(benzyloxy)carbonyl]), was obtained by means of Schollkopf bis-lactim ether methodology and optimized monoesterification procedures. Selective amino deprotection at the non-esterified amino-acid function of 7a by dichloromethyl-methyl-ether-induced 'N-carboxyanhydride' formation, and hydrolysis permitted access to the Boc/Cbz- and Fmoc/Cbz-protected monophenacyl esters 11a and 11b, as well as to the fully orthogonally protected Fmoc/Boc monophenacyl ester 12 (Boc = (teri-butoxy)carbonyl, Fmoc = (9H-fluoren-9-ylmethoxy)carbonyl).
The preparation of alkyl diamino dicarboxylic acids with high optical purity (100% ee, >98.5% de) and high yields based on asymmetric catalytic hydrogenation is described. The required prochiral precursors are prepared from dialdehydes and Z-, Boc-, and acetyl-protected phosphonoglycines. Aqueous solutions of glyoxal, succinic dialdehyde, and glutaric dialdehyde were used to prepare the diunsaturated
The yield of protected 2,7- diaminosuberic acid (DAS) prepared by Kolbe reaction of N-protected α-glutamic acid esters is dependent on solvent, temperature, concentration of carboxylate anion, and protecting groups. The highest yield of protected L,L-2,7-diaminosuberic acid is obtained with Boc-Glu-OMe as starting material using MeOH/pyridine/NaOMe as electrolyte.
Convenient preparative syntheses of differentially protected forms of (S,S)-2,7-diaminooctanedioic acid (2), suitable for application in peptide chemistry, are described. The key compound, the di-Cbz-protected phenacyl monoester 7a (Cbz = [(benzyloxy)carbonyl]), was obtained by means of Schollkopf bis-lactim ether methodology and optimized monoesterification procedures. Selective amino deprotection at the non-esterified amino-acid function of 7a by dichloromethyl-methyl-ether-induced 'N-carboxyanhydride' formation, and hydrolysis permitted access to the Boc/Cbz- and Fmoc/Cbz-protected monophenacyl esters 11a and 11b, as well as to the fully orthogonally protected Fmoc/Boc monophenacyl ester 12 (Boc = (teri-butoxy)carbonyl, Fmoc = (9H-fluoren-9-ylmethoxy)carbonyl).