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

1,3-Dipolar Cycloaddition of Methyl Pheophorbide-a and Synthesis of Chlorophyll Derivative

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,1HNMR及元素分析证明其结构.

From methyl pheophorbide-a （MPa, 1）, the pheophorbide-a derivative substituted with hydropyrazol 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 derivatives 246 were characterized by elemental analysis, UV, IR and 1H NMR spectra.