Synthesis of Orthogonally Protected (2<i>S</i>)-2-Amino-adipic Acid (α-AAA) and (2<i>S</i>,4<i>R</i>)-2-Amino-4-hydroxyadipic Acid (Ahad)
作者:Saroj Yadav、Carol M. Taylor
DOI:10.1021/jo400558t
日期:2013.6.7
(2S,4R)-2-Amino-4-hydroxyadipic acid (Ahad) building block 45 was synthesized in 11 steps and 6.5% overall yield from commercially available materials. Key steps in stereocontrol were an asymmetric conjugate addition employing a proline-based catalyst and a syn-selective intramolecular-conjugate addition of an oxygen nucleophile to an alpha,beta-unsaturated ester. To enable incorporation of alpha-amino-adipic acid (alpha-AAA) and Ahad into peptides, a truly orthogonal protecting group scheme was developed, encompassing an allyloxycarbonyl (Alloc) carbamate for Na, a tert-butyl ester for the delta-COOH, an acetol ester for the alpha-COOH, and a tert-butyldimethylsilyl ether for the gamma-hydroxy group of Ahad.
(2S,4R)-2-氨基-4-羟基己二酸(Ahad)结构单元45由市售材料经11步反应、6.5%的整体收率合成。手性控制的关键步骤包括采用脯氨酸基催化剂进行的不对称共轭加成,以及氧亲核试剂对α,β-不饱和酯的syn选择性分子内共轭加成。为了实现α-氨基己二酸(α-AAA)和Ahad在肽中的掺入,开发了一种真正正交的保护基方案:包括用于N-端的烯丙氧基羰基(Alloc)碳酸酯、用于δ-羧酸的叔丁氧基酯、用于α-羧酸的乙酰氧基酯以及用于Ahad中γ-羟基的叔丁基二甲基硅醚保护基。