Abstract
A convenient and efficient synthesis of novel achiral and chiral heterocyclic amino acid-like building blocks was developed. Regioisomeric methyl 5-(N-Boc-cycloaminyl)-1,2-oxazole-4-carboxylates were prepared by the reaction of β-enamino ketoesters (including azetidine, pyrrolidine or piperidine enamines) with hydroxylamine hydrochloride. Unambiguous structural assignments were based on chiral HPLC analysis, 1H, 13C, and 15N NMR spectroscopy, HRMS, and single-crystal X-ray diffraction data.
Highlights
Unnatural heteroarene amino acids have been widely used as building blocks to prepare various heterocyclic peptides [1722]
This study aimed to develop and synthesize methyl 5-(cycloaminyl)-1,2-oxazole-4-carboxylates, as new amino acid-like building blocks
The synthetic strategy for the synthesis of novel functionalized 1,2-oxazole derivatives is outlined in Scheme 1
Summary
Unnatural heteroarene amino acids have been widely used as building blocks to prepare various heterocyclic peptides [1722]. We have developed efficient protocols that provide easy access to highly functional heterocyclic compounds as novel amino acid-like building blocks by combining thiazole, selenazole, pyrazole, indazole, and indole moieties with both carboxyl functional groups and cycloaminyl units [27,28,29,30,31]. The synthetic route starts from the condensation of 1,3-diketones with N,N-dimethylformamide dimethylacetal to form β-enamino ketoester The latter undergoes a subsequent cycloaddition reaction with hydroxylamine to form regioisomerically substituted 1,2-oxazoles [34,35]. This study aimed to develop and synthesize methyl 5-(cycloaminyl)-1,2-oxazole-4-carboxylates, as new amino acid-like building blocks. This type of functionalized heterocycles could exhibit useful biological properties, and find appli-
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