作者:Benson J. Edagwa、Carol M. Taylor
DOI:10.1021/jo900459f
日期:2009.6.5
(+/-)-Dehydroleucine was prepared and resolved by porcine kidney acylase. Under the conditions of the Sharpless asymmetric dihydroxylation (SAD), employing AD-mix-alpha N alpha-carbobenzyloxy-(2S)-4,5-dehydroleucine methyl ester (16) gave rise to a 6.5:1.0 mixture of gamma-lactones 17, favoring the 4R configuration. Such carbamate-protected alpha-amino-gamma-hydroxylactones are not recommended as intermediates for peptide synthesis, since model studies showed that lactone 13 was unreactive toward an-Lines. Moreover, the lactone ring could not be opened hydrolytically without epimerization at C alpha. N alpha-Carbobenzyioxy-(2S)-4,5-dehydroleucine (22) was condensed with valine ethyl ester (19) to give dipeptide 23. Treatment of 23 with AD-ntix-beta, under the SAD conditions, converted the dehydroleucine residue to gamma,delta-dihydroxyleucine with 4S configuration, as occurs in alloviroidin (3), a natural product isolated from Amanita suballiacea.
(±)-脱氢亮氨酸的制备及拆分通过猪肾酰酶完成。在夏普莱斯不对称二羟基化(SAD)条件下,使用AD-mix-alpha,α-羧苄氧基-(2S)-4,5-脱氢亮氨酸甲酯(16)生成了6.5:1.0比例的γ-内酯(17),主要为4R构型。这种羰基保护的α-氨基-γ-羟基内酯不建议作为肽合成的中间体,因为模型研究表明,内酯13对α-氨基酸无反应性。此外,内酯环在α位不发生环状水解。α-羧苄氧基-(2S)-4,5-脱氢亮氨酸(22)与缬氨酸乙酯(19)缩合生成二肽(23)。将23与AD-mix-beta在SAD条件下处理,将脱氢亮氨酸残基转化为具有4S构型的γ,δ-二羟基亮氨酸,如alloviroidin(3)(源自Amanita suballiacea的天然产物)。