The Complete Stereostructure of Capsidiol. X-Ray Analysis and ¹³C Nuclear Magnetic Resonance of Eremophilane Derivatives Having trans-Vicinal Methyl Groups

Abstract

T o define the stereochemistry of capsidiol (I), an antifungal sesquiterpene isolated from sweet peppers, a detailed 13C n.m.r. investigation was carried out. From the results for 1 and a series of its derivatives (2-6) compared with those for several well-defined model compounds (7-21) it has been established that the vicinal methyl groups are trans, in contrast to all other previously described eremophilanes. This was confirmed by an X-ray structure analysis of 1 which also established the stereochemistry of the isopropenyl group as well as the detailed conformations of the two rings.The I3C spectra for the series 1-21 have been completely analyzed and these results are discussed in terms of the observed substituent effects. Further evidence of deshielding syn-axial 6 effects is presented.On a rCalise une ttude dttaillCe par r.m.n. de 13C afin de definir la stCrCochimie du capsidiol (I), un sesquiterpene fongicide extrait des piments doux. Par comparaison des risultats obtenus avec 1 et une sCrie de ses dCrivCs ( 2 4 ) avec ceux obtenus pour plusieurs composCs modeles bien dtfinis (7-21) on a pu Ctablir que les groupes mCthyles vicinaux sont trans et ceci en opposition avec tous les eremophilanes dkcrits antkrieurement. Ce rtsultat a CtB confirm6 par une analyse structural aux rayons-X de 1 qui a aussi Ctabli la stertochimie du groupe isopropCnyle de meme que les conformations dCtaillkes des deux noyaux.Les spectres 13C pour tous les composes 1-21 ont CtC cornpletement analysks et ces rksultats sont discutis en termes des effets de substituents qui ont et6 observks. On presente des preuves supplCmentaires au sujet des effets de deblindages syn-axial 6.[Traduit par le journal]Can. J. Chem., 52,993 (1974)

The Structures of some Stress Metabolites from Solanummelongena

“…upfield from the corresponding signal for 7. This difference agreed very nicely with that predicted from the results for 12 and 13 (17). The angular methyl shieldimgs for the latter pair differ by 3 p.p.m.…”

“…Selective decoupling using a C6D6 solution of 7, identified the individual signals for the angular and secondary methyl carbons and the latter's shielding (13.4 p.p.m.) is as expected for methyl a to carbony1 (16) while the value for the angular methyl seemed to be in good agreement with that expected for C-15 in structure 7 on the basis of the gvailable data for angular methyl carbons in related trans-decalones (17). However, it seemed worthwhile to determine the methyl shielding in a better model system and to this end we prepared olefin 11 as described in the accompanying paper (18).…”

Toxic Furanoeremophilanes from Senecio bonariensis

“…Trans A/B ring stereochemistry was supported by reported data for cis-and trans-decalin (Dalling et al, 1973;Gough et al, 1972), comparison with cis-and trans-decalones (Birnbaum et al, 1974) and 3-substituted 9-oxo-10␣H-furanoeremophilane data (Chalmers et al, 1980). Chemical shifts of A-ring carbons were calculated taking into account methyl substituent parameters for substituted cyclohexanes (Dalling and Grant, 1972) adding deshielding ␤-effect of a carbonyl group.…”

Functional Characterization of Premnaspirodiene Oxygenase, a Cytochrome P450 Catalyzing Regio- and Stereo-specific Hydroxylations of Diverse Sesquiterpene Substrates

“…The two large couplings indicate axial orientations of H1, H2, and H3, and the two intermediate couplings arise from further axial-equatorial interactions between H1-H2 and H2-H3. The preferred conformation of the A ring of epiaristolochene is a half-chair with the vicinal methyl groups in axial positions (31). Thus the hydroxyl group at C-2 was assigned an equatorial disposition.…”