New Synthetic Method for Dehydrotryptophan Derivatives. Synthetic Studies on Indoles and Related Compounds. XXXIV.
作者:Yuusaku YOKOYAMA、Makio TAKAHASHI、Mitsuru TAKASHIMA、Yukari KOHNO、Hideki KOBAYASHI、Kazutaka KATAOKA、Kazuko SHIDORI、Yasuoki MURAKAMI
DOI:10.1248/cpb.42.832
日期:——
Dehydrotryptophans (9) having various substituents on the indole ring were synthesized by vinylation of the corresponding indole derivatives (6) with N-acetyldehydroalanine methyl ester (7a) by the use of a stoichiometric amount of palladium salt in acetic acid (stoichiometric condition). Although vinylation of 4-, 5-, and 7-bromoindoles (6b, g, l, m) with 7a occurred chemoselectively at the C3-position to give the corresponding bromodehydrotryptophans (9b, g, l, m) under the stoichiometric condition, the palladium-catalyzed vinylation of 4-bromoindoles (6b, i) occurred at the bromine-bearing carbon at the C4-position [0.1 eq PdCl2(PPh3)2 in Et3N-dimethylformamide]. Vinylation of 3-bromoindoles (17a, b) with 7a, or ethoxycarbonyl-(7b) or tert-butoxycarbonyldehydroalanine methyl ester (7c) also gave the dehydrotryptophan (18a-d) in good yields under catalytic conditions. One of two possible regioisomers of the vinylated products was isolated in all cases, and the geometry was determined as Z based on the coupling constant of the ester carbonyl carbon and the olefinic proton in the 13C-NMR spectrum.
通过将相应的吲哚衍生物(6)与N-乙酰脱氢丙氨酸甲酯(7a)在乙酸中使用化学计量的钯盐(化学计量条件)进行乙烯基化,合成了在吲哚环上带有各种取代基的脱氢色氨酸(9)。尽管在化学计量条件下,4-、5-和7-溴吲哚(6b、g、l、m)与7a在C3位置上发生化学选择性乙烯基化,生成相应的溴脱氢色氨酸(9b、g、l、m),但钯催化的4-溴吲哚(6b、i)的乙烯基化发生在C4位置上带溴的碳上[0.1 eq PdCl2(PPh3)2 在Et3N-二甲基甲酰胺中]。3-溴吲哚(17a、b)与7a或乙氧羰基(7b)或叔丁氧羰基脱氢丙氨酸甲酯(7c)的乙烯基化在催化条件下也以良好产率生成脱氢色氨酸(18a-d)。在所有情况下,分离出两种可能的区域异构体中的一种,根据13C-NMR谱中酯羰基碳和烯烃质子的耦合常数,几何构型确定为Z。