Minor alkaloids of Tylophora hirsuta

Seven minor alkaloids have been isolated from Tylophora hirsuta. The known alkaloids 14-hydroxyisotylocrebrine, (+)-isotylocrebrine, (−)-tylophorine and 4-desmethylisotylocrebrine have also been isolated in addition to three new alkaloids, namely 14-desoxy-13a-methyltylohirsutinidine, 5-hydroxy-O-methyltylophorinidine and tylohirsuticine. Structural studies indicate that the first six alkaloids possess the dibenzo-f,h]pyrrolo1,2b]isoquinoline skeleton but differ in the number, nature and distribution of the oxygen-bearing substituents, in the presence or absence of a benzylic type hydroxyl and an angular methyl function. Tylohirsuticine possesses a related septicine-type skeleton containing four oxygen-bearing substituents on the cleaved phenanthrene nucleus and an angular methyl function.