Imidazolone and Imidazolidinone Artifacts of a Pivotal Imidazolthione,Zyzzin, from the poecilosclerid sponge Zyzza massalis from the coral sea. The first thermochromic systems of marine origin

Dry acetone extracts of the freeze-dried, deep-red powder of the poecilosclerid sponge Zyzza massalis (DENDY ) from the Coral Sea gave the orange alkaloid zyzzin (= 4-(1H-indol-3-yl)-1,5-dihydro-5-thioxo-1H-imidazol-2-one 14 ), which underwent exchange of the 5-thioxo for the 5-oxo group during aqueous chromatographic workup, giving yellow 13 . Both 13 and 14 added hydroxylic solvents at C(4)=N giving colourless, racemic products, 3 and 8 , respectively, by incorporation of MeOH and 10 and 11 , respectively, by incorporation of H₂O. On warming 3 or 10 in DMSO, 13 was recovered, thus furnishing a novel thermochromic system. Optically active (+)- 12 , which may be viewed to derive from enzymatic reduction of 14 at C(4)=N followed by S→O exchange, was also isolated from this sponge, along with the linear amides 16 and 19 . Compound 3 proved to have antibacterial and antifungal activities.