a 3S-hydroxy-4S-iodo-(L)-pipecolic acid or a 3R-hydroxy-4R-iodo-(D)-pipecolic acid residue, which were separated by thin layer chromatography. Assignment of configuration was unambiguous when the synthesis was repeated with (L)-baikiain as starting material. All compounds exhibited conformational isomerism in their1H NMR spectra, attributed to the existence of boths-cis ands-trans configurations of
(D,L)-拜甲
氨酸甲酯与Boc-(L)-苯丙
氨酸偶联,然后通过(L)-异亮烷基-(L)-缬
氨酸甲酯对非对映异构体
碘代内酯进行皂化,偶氮内酯化和
氨解,得到两个掺入了非对映异构体的肽无论是3 š羟基-4小号-
碘(L)-pipecolic酸或3 - [R -羟基-4 - [R -
碘(d)-pipecolic酸残基,这是由薄层色谱法分离。当以(L)-baikiain为起始原料重复合成时,构型的分配是明确的。所有化合物在其1 H NMR光谱中均显示出构象异构现象,这归因于同时存在s-顺式和s-反式Phe-NR 2肽键的构型。两个分离的非对映异构体中的每一个的乙酰化得到Boc-(L)-Phe-3 S -OAc-4 S -I-(L)-Pip-(L)-Ile-(L)-Val-OMe和Boc-( L)-Phe-3 R -OAc-4 R -I-(D)-Pip-(L)-Ile-(L)-Val-OMe。N-脱保护并通过
DCC