Conformations of ten-membered-ring sesquiterpenes. Crystal and molecular structures of agerol diepoxide and ageratriol

Abstract

The crystal and molecular structures of agerol diepoxide (3) and ageratriol (2), which have been determined by direct methods and refined by least-squares to R 0.060 and 0.069 respectively, confirm the previously suggested biogenetic scheme from agerol (1 ). Theoretical calculations by a molecular mechanics method ( G E M 0 program) show that the conformers observed in the crystals have the lowest strain-energy. N.m.r. measurements indicate that agerol diepoxide adopts this conformation also in solution.AGEROL (1) and ageratriol (2) are the main sesquiterpene configurations have been determined by chemical components of Achzillea ageratum, and their absolute methods.lP2 Chemical transformation of the diepoxide

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“…The structures of agerol diepoxide and ageratriol, established by X-ray analysis by Messerotti et al (287), confirmed the previously suggested biogenetic scheme from agerol.…”

Structures and conformations of (–)-isobicyclogermacrenal and (–)-lepidozenal, two key sesquiterpenoids of the cis- and trans-10,3-bicyclic ring systems, from the liverwort Lepidozia vitrea : X-ray crystal structure analysis of the hydroxy derivative of (–)-isobicyclogermacrenal

“…and 'H n.m.r. spectra with those of the authentic specimen prepared by isonierization of the natural (4-)-bicyclogermacrene (25), an enantiomer of ( -)-enr-bicyclogermacrene (4)." The geometries of the two double bonds were alternatively shown to be C(I)-C(l0) trans and C(4)-C(5) cis on the basis of n.0.e.…”

“…863 cm-I; 6 1. 25 (3 H, d, J 1.5 Hz) and 5.06 (1 H, m)] and a cyclopropane ring with a gem-dimethyl group [v,,,,,. 1 382 and 1 377 cm-'; 6 0.1-1.1 (2 H, m) and 1.18 and 1.21 (each 3 H, s)].…”

“…15 and 1. 25 (each 3 H, s)] and a formyl group conjugated with a trisubstituted double bond [h,,,, 265 nm; v, , , , , , I 685 and I 630 cm-I; 6 6.33 ( I H, d, J 10.0 Hz) and 9.30 ( I H, s)] along with another trisubstitated double bond with a methyl group [vI,,<,, 870 cni-I; 6 1.64 (3 H, d, J I .5 Hz) and 5.05 ( 1 H, m)]. A close similarity between the spectral properties of the first aldehyde ( I ) and those of the second (2) suggested that the two were stereoisomers with respect to one of the three geometries on the two double bonds and one cyclopropane ring existing in both the molecules of cyclodeca-l,5-diene fused with a cyclopropane.…”

Nmr Studies of Tatridin A and Some Related Sesquiterpene Lactones from Tanacetum vulgare

“…Hz) indicate an anti coplanar relationship between -1 and one of these hydrogens (H-2 or H-2'), i.e., an axiallike orientation for -1. The conformation ofgermacrane derivatives, however, is often very difficult to determine, due to the flexibility of medium-sized rings (17)(18)(19). In the case of compound 1, for instance, an axial-like orientation of -1 can be reached with both possible configurations at C-l.…”