氢氧化锂存在下(焦)脱镁叶绿酸-a甲酯的空气重排反应

在氢氧化锂存在下, 脱镁叶绿酸-a甲酯(1a)发生空气氧化和重排反应, 经盐酸酸化和重氮甲烷甲基化, 得到由紫红素-7三甲酯(2)、紫红素-18甲酯(3)、卟吩-p₆三甲酯(4)、地质卟啉衍生物(5)和3-环氧乙基-3-去乙烯基紫红素-18甲酯(6)所组成的混合物. 用相同的方法处理焦脱镁叶绿酸-a甲酯(1b), 则分离出13²-氧代焦脱镁叶绿酸-a甲酯(7)、15-甲酰基紫红素-5二甲酯(8)、紫红素-18甲酯(3)和3-环氧乙基-3-去乙烯基紫红素-18甲酯(6). 所得新叶绿素衍生物5, 6和8的化学结构均经UV, IR, ¹H NMR及元素分析得以证实, 并对相应的反应提出可能的反应机理.

Air Oxidation and Rearrangement Reactions of Methyl(pyro)-pheophorbide-a in the Presence of Lithium Hy-droxide

In the presence of lithium hydroxide, air oxidation and rearrangement reactions of methyl pheo-phorbide-a (1a) followed by acidification with hydrochloric acid and methylation with diazomethane to give a mixture including purpurin-7 trimethyl ester (2), purpurin-18 methyl ester (3), chlorine-p6 trimethyl ester (4), geoporphyrin derivatives (5) and 3-epoxyvinyl-3-devinylpurpurin-18 ester (6) were performed. Methyl pyropheophorbide-a (1b) was oxidized in the same reaction as chlorin 1a followed by chromatography isola-tion to obtain methyl 132-oxopyropheophorbide-a (7), 15-formylpurpurin-5 dimehyl ester (8), purpurin-18 methyl ester (3) and 3-epoxyvinyl-3-devinylpurpurin-18 ester (6), respectively. The structures of new chlo-rophyll derivatives 5, 6 and 8 were characterized by UV, IR, 1H NMR spectra and elemental analysis. The possible mechanisms for the air oxidation and rearrangement reaction were tentatively proposed.