叶绿素-a及其衍生物的Qy轴向氧化反应和E-环重排反应

在酸碱性条件下对叶绿素-a (1)进行空气氧化反应, 分别得到卟吩衍生物2b～4b; 通过酯交换和去金属镁离子, 将叶绿素-a转化为脱镁叶绿酸-a甲酯(MPa) (5), 其3-位碳碳双键与氯化氢的加成生成卟吩醇(6), 经碱性空气氧化和E-环重排则转化成紫红素-18衍生物7. 选用四氧化锇和高碘酸钠将5氧化成卟吩醛(8), 在丁醇中以丁醇钠作催化剂, 8的氧化和重排反应给出3-甲酰基紫红素-18酯(9)和紫红素-7三甲酯衍生物10. 异构体4的空气氧化和重排反应也生成紫红素-18酯(3), 进一步与2-甲基丁胺进行缩合反应, 得到N-烷基紫红素-18酰亚胺(11a)以及氧化重排产物3-甲酰基-N-烷基紫红素-18酰亚胺(11b). 所得叶绿素衍生物均经UV, IR, 1H NMR及元素分析证明其结构, 并对相应的反应提出可能的反应机理.

Oxidation Reaction along Qy Axis and Rearrangement Reaction in

The chlorophyll-a (1) was converted into the chlorins 2b～4b by air-oxidation in acid or basic condition. The methyl pheophorbide-a (5) was obtained from chlorophyll-a by transesterification and demetallation. The addition to double bond at 3-position of 5 with hydrochloric acid yielded alcohol chlorin 6 which was oxidized purpure-18 derivative (7) by air-oxidation in basic condition. The methyl pheophorbide-a (5) was oxidized with osmium oxide and sodium periodate to give chlorin 8 which was converted into aldehyde purpure-18 (9) and purpure-7 trimethyl ester (10) by air-oxidation in butanol in the presence of sodium. The purpure-18 ester (3), prepared also from the pheophorbide-a (4) in the same reaction condition like the chlorophyll-a (1), reacted with 2-methylbutylamine to give N-(2-methylbutyl)-purpure-18 imide (11a) and 12-formyl-purpure-18 imide (11b). The structures of all chlorophyll derivatives were characterized by UV, IR, 1H NMR spectra and elemental analysis. The possible mechanisms in accordance with the corresponding chemical reaction and reaction condition were tentatively proposed.