(2S,3S)-2-Acetoxy-3-methylvaleric acid (3) is prepared from L-isoleucine (2) with 96% retention of configuration. Compound 3 is converted to optically pure methyl D-alloisoleucinate (7) as its hydrochloride salt, via the methanesulfonate 5 and the azide 6 with 76% yield and 99.9% inversion. Subsequent protection-saponification-activation of 7, followed by reaction with the lithium enolate of methyl trimethylsilyl malonate and reduction, yields (3S,4R,5S)-N-(9-fluorenylmethoxycarbonyl) isostatine (12). (3S.4R,5S)-Isostatine is a characteristic unit of the didemnines 1.
(2S,3S)-2-乙酰氧基-
3-甲基戊酸(3)是通过
L-异亮氨酸(2)制备的,保留构型率为96%。化合物3转化为光学纯的甲基D-全
异亮氨酸盐酸盐(7),经过
甲烷磺酸酯5和
叠氮化合物6,产率为76%,反转率为99.9%。随后对7进行保护-皂化-活化反应,再与甲基三甲基
硅基
丙二酸锂烯醇盐反应并还原,得到(3S,4R,5S)-N-(9-
芴甲氧基羰基)
异亮氨酸(12)。(3S,4R,5S)-
异亮氨酸是二
氟氮碱1的特征单元。