ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Peptide-Bond Formation with C-Terminal α,α-Disubstituted α - Amino Acids via Intermediate Oxazol-5(4H)-onesThe formation of peptide bonds between dipeptides 4 containing a C-terminalα,α-disubstituted α-amino acid and ethyl p-aminobenzoate (5) using DCC as coupling reagent proceeds via 4,4-disubstituted oxazol-5(4H)-ones 7 as intermediates (Scheme 3). The reaction yielding tripeptides 6 (Table 2) is catalyzed efficiently by camphor-10-sulfonic acid (Table 1). The main problem of this coupling reaction is the epimerization of the nonterminal amino acid in 4 via a mechanism shown in Scheme 1. CSA catalysis at 0° suppresses completely this troublesome side reaction. For the coupling of Z-Val-Aib-OH (11) and Fmoc-Pro-Aib-OH (14) with H-Gly-OBu1 (12) and H-Ala-Aib-NMe2 (15), respectively, the best results have been obtained using DCC in the presence of ZnCl2 (Table 3).
Additional Material:
3 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19860690524
