Viriditoxin

Viriditoxin (VDT ) is a secondary metabolite produced by fungi. Viriditoxin is a type of mycotoxin. The biosynthesis of the compound has been investigated.

Occurrence
It is produced by several Aspergillus species including A. aureoluteus, A. brevipes, and A. viridinutans in which it was first identified in 1971. It has been isolated from Paecilomyces variotii, which was obtained from Nomura's jellyfish. It is also produced by Cladosporium cladosporioides.

Structure
Natural viriditoxin exists as a single atropisomer owing to restricted rotation about the C-C bond which joins the two naphthol rings. It has been confirmed by total synthesis to be twisted into the so-called M isomer.

Biosynthesis
Viriditoxin is a secondary metabolite, a polyketide produced from multiple acetyl-CoA and malonyl-CoA units which are combined by a polyketide synthase (PKS) enzyme complex. A chain of eight acetate units are cyclised to give the three-ring system which forms half of the carbon framework of the final product. After selective methylation of one of the phenol groups and reduction of the pyrone ring, the resulting intermediate (semiviriditoxin) is dimerised by a laccase enzyme, generating specifically the minus M atropisomer.

Uses
In nature, viriditoxin likely is used against microbial competition. On mangroves, P. variotii 's production of viriditoxin was linked to antagonism against bacteria.