脱镁叶绿酸-a甲酯的1,3-偶极环加成及其叶绿素衍生物的合成

以脱镁叶绿酸-a甲酯(1)为起始原料, 利用其3-位乙烯基与重氮甲烷的1,3-偶极环加成反应, 得到3-位氢化吡唑取代的脱镁叶绿酸-a衍生物2, 通过热裂解使得3-位吡唑基开环并重排成环丙基. 碱性条件下, 所生成的3-环丙基取代的卟吩3脱甲氧甲酰基后转化成焦脱镁叶绿酸衍生物4. 选用重氮乙烷为另一偶极体与1进行1,3-偶极环加成反应, 则给出2-甲基环丙基取代的立体异构体卟吩5, 同样经过脱甲氧甲酰基处理, 得到焦脱镁叶绿酸衍生物6. 所合成新叶绿素衍生物2～6均经UV, IR, ¹H NMR及元素分析证明其结构.

1,3-Dipolar Cycloaddition of Methyl Pheophorbide-a andSyn-thesis of Chlorophyll Derivative

From methyl pheophorbide-a (MPa, 1), the pheophorbide-a derivative substituted with hydro-pyrazol 2 was obtained by the 1,3-dipolar cycloaddition of vinyl group at 3-position with diazomethane. Ring opening of this chlorin was performed by heating to rearrange the hydropyrzaol ring into the cyclopropyl group. In basic condition the cyclopropyl-substituted chlorin 3 was converted into pyropheophorbide 4 by demethoxyformylation. The diazoethane was chosen as another dipole and reacted with chlorin 1 in 1,3-dipolar cycloaddition style to give 2-methylcyclopropyl-substituted stereoisomer chlorin 5. The treatment for demethoxyformylation like chlorin 2 yielded pyropheophorbide 6. The structures of all new chlorophyll-a deriva-tives 2～6 were characterized by elemental analysis, UV, IR and ¹H NMR spectra.