Farnesane sesquiterpenes

Alcohol 2.1 is the only example of this class, and was isolated from Lactarius camphoratus (79) which belongs to Section Olentes (2). The compound is presumably the product of 1-9 cyclization of a humulene precursor. The structure and absolute configuration of this new caryophyllene oxide (2.1) was determined by a combination of spectral data and a single-crystal X-ray analysis of the p-bromobenzoate derivative 2.3. The NMR spectrum of 2.1 exhibited only two methyl signals, one of them at 51.20, together with one-proton doublet of doublets centred at 52.93, strongly suggesting the presence of the 4,5-epoxide. The C-12 methylene protons were shifted downfield (5 3.84) in the 220 MHz NMR spectrum of the acetyl derivative (2.2). Moreover, 

Compound 2.1 is one of the very few examples of sesquiterpenes from Lactarius, where one of the geminal methyl groups occurring in all skeletons has been oxidized to a hydroxy methylene function. 

A strong positive Cotton effect at 320 nm in the CD spectra of uvidin A (3.5) and B (3.6) indicated the P-configuration of the epoxy ring, according to the anti-octant rule for ocP-epoxyketones (20). 

Exposure of uvidin A (3.5) or the mixture of uvidin A esters to methanolic KOH led to the new lactone 3.38, arising by a Favorski-like rearrangement of the a,P-epoxyketone group. The same rearrangement was also observed for 11-0-ethoxyethyl uvidin A however, in this case, the formation of the lactone ring involved the tertiary C(7)-OH group of compound 3.39. Compounds 3.38 and 3.39 have a new sesquiterpenoid skeleton named isothapsane (22). 

Uvidins are attractive chiral starting materials for the synthesis of highly oxidized biologically active drimane-like sesquiterpenes, as already demonstrated by the syntheses of natural (—)-cinnamodial 23) and (—)-cinnamosmolide 24) from uvidin A (3.5). 

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Recently, the farnesane sesquiterpenes 1.1-1.9 (Table 1) have been isolated for the Brst time from Lactarius porninsis, the only species of the Section Zonarii investigated so far (8). Pominsal (1.1), porninsol (1.2) and the esters 1.3-1.9 show a high thermal and photochemical lability because of the conjugated tetraene system and readily polymerize when their solutions are taken to dryness. Therefore, special mild conditions are required for their isolation and for recording the spectroscopic data. The composition of the ester mixture 1.3-1.9 was established by capillary GC and GC-MS analysis of the methyl esters obtained by transesterification (8). 

Gamba-Invernizzi, A., L. Garlaschelli, A. Rossi, G. Vidari, and P. Vita-Finzi New Farnesane Sesquiterpenes from Lactarius porninsis. J. Nat. Prod., 56, 1948 (1993). 

Drimane, farnesane, glutinopallane, protoilludane, isolactarane, and guaiane sesquiterpenes have been isolated so far in a few Lactarius species therefore, they may be considered chemotaxonomic markers. By contrast, large quantities of marasmane, lactarane and secolactarane metabolites occur in almost all Sections, as reported in Table 24. 

Undoubtedly one of the major highlights in the sesquiterpenoid field this year has been the very interesting results concerning the co-occurrence patterns and in vitro conversions of sesquiterpenes within the farnesane,bisabolane,curcumane, acorane, alaskane, cedrane, and zizaane groups. For instance, Kaiser and... 

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