In the search for novel bioactive products from filamentous fungi, sterols and triterpenoids found in Phycomyces blakesleeanus were analyzed using semipreparative HPLC, GC-MS, and NMR techniques. Structures proposed for the three new compounds identified, phycomysterol A (1), phycomysterol B (2), and neoergosterol (3), were confirmed by chemical synthesis. Phycomysterols possess a new natural 19-norergostane skeleton with an aromatic B ring. Phycomysterol A showed anti-HIV activity.Fungi have been one of the main natural sources of biologically active substances since the discovery of antibiotics. Searching for new bioactive products from filamentous fungi, chemical analysis and biological screening of metabolites from Gibberella fujikuroi have been the subject of our work over the past few years. [1][2][3] We recently began studying Phycomyces blakesleeanus (Mucoraceae), which is a fungal producer of -carotene (provitamin A), riboflavine (vitamin B 2 ), pyridoxine (vitamin B 6 ), ergosterol (provitamin D 2 ), biotin, and nicotinic acid. 4,5 Therefore, oil from Phycomyces could be an interesting alimentary vitamin complement, if it were proven to be free of mycotoxins. We have identified more than forty nontoxic compounds among the acidic metabolites from P. blakesleeanus 6 and are now working on neutral metabolites. In the mycelium of P. blakesleeanus (NRRL1555 wild strain) we have found eleven sterols previously unreported in Phycomyces. These include the new natural sterols (1-3; Chart 1) with a 19-norergostane skeleton and an aromatic B ring. Previous studies of sterols from Phycomyces at the University College of Wales yielded a number of new sterols (4-13) and certain aspects of fungal ergosterol biosynthesis were resolved. 7-11 However, some sterols present in the fungus were not identified. 9 Results and DiscussionSterol and triterpene mixtures isolated from P. blakesleeanus were subjected to semipreparative HPLC. Fractions obtained were studied by NMR spectroscopy and aliquots were treated with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) to form TMS derivatives for analysis by GC-MS. The sterol ester mixture was saponified, and the nonsaponifiable fraction was analyzed as described above. Results are shown in Table 1. Proportions are only approximate because they were determined from the area of the gas chromatogram peaks, based on total ion current response data. TMS-ethers of sterols were used for GC-MS analysis, instead of free sterols, because the former have better chromatographic properties and afford highly characteristic modes of fragmentation from which structural details may be inferred. 12 In the mass spectrum of 1, as the TMS-ether, the molecular ion was consistent with the TMS derivative of a sterol with the molecular formula C 27 H 40 O, containing four double bonds. The fragment ions [M -TMSOH -C 9 H 17 ] + , [M -TMSOH -C 6 H 11 ] + , and [M -(C 6 H 11 + H)] + indicated a side chain with nine carbon atoms and a double bond. Thus, 1 must possess a nucleus with three double bonds and ...