Lactarane sesquiterpenes

Furantriol (18.27), isolated from L. mitissimus (84), is one of the few lactarane sesquiterpenes in which one of the gem-methyl groups at C-11 is oxidized and it was chemically correlated (82) with lactarorufin B (11.71), another example of this kind. The Polish authors suggested that lactone 11.71 was enzymatically formed from furan 18.27, and that a C-15 oxidized sesquiterpene of the velutinal type was the common precursor of both compounds in the mushroom (84). Actually, the possibility for the C-15 methyl group to be oxidized at an early stage of the lactarane biosynthesis seems to be confirmed by the recent finding of C-15 hydroxylated protoilludane sesquiterpenoids (5.1 and 5.2) in L. violascens (23) (Table 5). 

Noteworthy among these conversions are the first successful cyclizations of lactone and furan secolactaranes to the corresponding lactarane sesquiterpenes, which were obtained by a Me2AlCl catalysed ene reaction (60). Under these conditions lactaral (19.1) yielded directly the diene 18.1, identical with the dehydration product of furosardonin A (18.8), while smooth cyclization of aldehyde 14.3 gave the lactone 11.8 in which the protons H-8 and H-9 have the "unnatural" cis stereochemistry. This result could be anticipated by examination of the Dreiding models of the two possible transition states 11.8 A and 11.8 B, which showed that unfavourable steric interactions developing between the C-3 methyl group and the bulky >C=0-—AI J complex are minimized in the... 

Flavidulol D was isolated from L. flavidulus, and its structure was identified as the stearate of flavidulol A (22.8) on the basis of spectroscopic data (147). The new marasmane lactone P3 and diketopiperazine P4 were isolated from the most polar fraction of an ethanolic extract of L. vellereus (148). The structures of compounds P3 and P4 were established by extensive NMR studies together with acetylation reactions. The isolation of lactone P3 suggested that the possible oxidation of the 15-methyl group, typical of a few lactarane sesquiterpenes, could take place at the early velutinal stage... 

The total synthesis of (+)-furoscrobiculin B, a lactarane sesquiterpene isolated from basidiomycetes of mushrooms, was accomplished in the laboratory of H. Suemune and K. Kanematsu using a furan ring transfer reaction and a semipinacol rearrangement as key steps. The secondary hydroxyl group of the tricyclic c/s-vicinal diol substrate was converted to the corresponding tosylate that in situ underwent a ring-expansion reaction to afford an azulenofuran in good yield. 

The lactarane sesquiterpenes 10.2, 10.10, 10.13, containing the 2(9),7(8)-cycloheptadiene ring were submitted to conformational analysis by molecular mechanics and HNMR spectroscopy (9). It was observed that the conformational mobility of each compound is practically restricted to the interconversion of the envelope forms of the cyclopentene ring by contrast, essentially only a single conformation of the seven membered ring, with the 3-methyl group pseudo-equatorially oriented, is populated. This is due to the planarity of either the diene in 10.13 or the diene-carbonyl double bonds in 10.2, 10.10. 

Daniewski, W.M., M. Gumulka, K. Ptaszynska, G. Vidari, L. Garlaschelli, G. Fronza, and M. Budesinsky 7- pi-pipertriol, a Lactarane Sesquiterpene from Lactarius necator. Phytochemistry, 21, 3314 (1988). 

Garlaschelli, L., L. Toma, G. Vidari, and D. Colombo Conformational Studies and Stereochemical Assignments of the Lactarane Sesquiterpenes Furoscrobiculin D and Blennin D. Tetrahedron, 50, 1211 (1994). 

Bosetti, a., G. Fronza, G. Vidari, and P. Vita-Finzi Norlactarane and Lactarane Sesquiterpenes from Lactarius scrobiculatus. Phytochemistry, 28, 1427 (1989). 

Daniewski, W.M., M. Gumulka, P. Gluzinski, J. Krajewski, E. Pankowska, K. Ptaszynska, J. Sitkowski, and E. Bloszyk 3-Ethoxy Lactarane Sesquiterpenes of Lactarius Origin Antifeedant Activity. Polish J. Chem., 66, 1249 (1992). 

Zhang, J., and X.Z. Feng Subvellerolactone C, a New Lactarane Sesquiterpene from Lactarius subvellereus. Chin. Chem. Lett., 7, 1097 (1996). 

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