A naturally occurring pyrimidodiazepine in Drosophila: chemical and spectral properties and relationship to drosopterin.

The structure of an intermediate, in drosopterin biosynthesis, as 6-acetylpyrimidodiazepine has been confirmed by high-resolution mass spectra, 13C NMR, chemical ionization mass spectra, and chemical properties. A trivial name of 6-acetylhomopterin is suggested and should replace the term "quench spot" used heretofore. The structure of drosopterin includes, in part, a pyrimidodiazepine, a compound that consists of a fused six- and seven-membered heterocyclic ring system. Earlier studies demonstrated that 6-acetylhomopterin strongly stimulated the enzymatic synthesis of drosopterin and related eye pigments by preparations from Drosophila. The occurrence in nature is quite limited for diazepines; drosopterin and homopterin are the first examples in eukaryotes.