The structures of sclerosporin and its aldehydic congener, sclerosporal, have been revised as 1 and 2, respectively, on the basis of detailed spectral analysis of sclerosporal _ with 360 MHz 'H NMR and their total synthesis. Sclerosporin, a sporogenic substance isolated from Sclerotinia fructicola, dramatically induced the formation of asexual arthrospores in this fungal mycelium at a concentration of 1 ng/ml.l In our previous study,* the structures of sclerosporin and sclerosporal were believed to possess a gaiane skeleton. Evidence for the gaiane skeleton was derived from the close similarity in the mass spectra of the hydrocarbon, C1SH2B, which was chemically derivatized from sclerosporal through four steps of ultramicro-reactions, to those of authentic stereoisomers of guaiane. Since the structures previously postulated were deduced from very small amounts of sclerosporin (182 pg) and sclerosporal (194 ug) on the basis of the limited experimental data, we continued synthetic investigation to confirm the proposed structures.
This work revealed that the mass spectrum of trans-guaiane3 was almost indistinguishable from that of trans-cadinane (Fig. 1). Thus, our previous conclusion on the carbon skeleton based solely on the mass spectral comparison required reinvestigation.
We wish now to present the correct structures of sclerosporin and sclerosporal as 1 and 2, respectively, which were deduced by detailed spectral analysis of sclerosporal with 360 MHz 'H NMR.
This has now been confirmed unambigously by the total synthesis of both compounds.