A series of novel non-proteinogenic heterocyclic substituted α-amino acids derived from L-aspartic acid have been synthesised using the alkynyl ketone functionality as a versatile building block. Condensation of (S)-2-tert-butoxycarbonylamino-4-oxohex-5-ynoic acid tert-butyl ester 4 with enamines 5, 6, phenylhydrazine, hydroxylamine and phenyl azide has led to the generation of pyridines 9, 10, pyrazolines 11a/b, isoxazoles 12a/b, and triazole 13, respectively in moderate to excellent yields. Acid deprotection of the initial adducts afforded the desired heterocyclic substituted α-amino acids as their TFA salts or in the form of the zwitterions themselves after ion-exchange chromatography. The enantiomeric purity of a representative selection of these products were greater than 98% ee as verified by derivatisation to the corresponding Mosherâs amides and subsequent 19F NMR spectroscopy.
以炔基酮官能团为多功能构建基块,合成了一系列源自
L-天冬氨酸的新型非蛋白源杂环取代δ-
氨基酸。(S)-
2-叔丁氧羰基氨基-4-氧代己酮-5-炔酸叔丁酯 4 与烯胺 5、6、苯
肼、
羟胺和苯基
叠氮化物缩合后,分别生成了
吡啶 9、10、
吡唑 11a/b、
异噁唑 12a/b 和三唑 13,收率中等到极好。对初始加合物进行酸性脱保护处理后,可以得到所需的杂环取代的δ-
氨基酸作为其反式
脂肪酸盐,或在离子交换色谱法后以齐聚物的形式得到。通过衍生成相应的莫舍尔酰胺以及随后的 19F NMR 光谱分析,这些产品中具有代表性的对映体纯度超过 98%ee。