ZAPOTIDINE

Description

The seeds of Casimiroa edulis Llave et Lex yield this alkaloid which has the unusual structure of 6-methylimidazc 1 ,5-c tetrahydropyrimidine-5-thione, a type of ring system not previously encountered in a natural product, it being rare for thiourea derivatives such as this to occur in nature. Zapotidine has been characterized as the picrate which forms yellow laths when crystallized from MeOH and has m.p. 195-6°C. The free base gives an ultraviolet spectrum having absorption maxima at 237,256 and 290 nm. Catalytic hydrogenation with Ptf AcOH has proved unsuccessful but when reduced with LiAIH4 , the alkaloid furnishes N,N-dimethylhistamine, giving a dipicrate with m.p. 23l-3°C. Boiling with ethanolic silver nitrate accompanied by the gradual addition of aqueous sodium hydroxide yields the urea derivative, C7H9N03, m.p. 11 5-6°C in which the sulphur is replaced by oxygen. When boiled with 20 per cent aqueous potassium hydroxide in EtOH, zapotidine gives N-methylhistamine characterized as the dipicrate, m.p. l88-l90°C. Biogenetically, it is possible that the alkaloid is formed by ring closure of I-acetyl (or thioacetyl)-histamine followed by methylation.

References

Kincl et at., J. Chem. Soc., 1463 (1956) Mechoulam et al., J. Amer Chem. Soc., 83, 2022 (1961)