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New guaianolides from Berlandiera Pumila and B. Texana , and the X‐ray crystal structure of pumilin
Author(s) -
Korp James D.,
Bernal Ivan,
Fischer Nikolaus H.,
Leonard Charles,
Lee IhlYoung,
LeVan Ngo
Publication year - 1982
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570190135
Subject(s) - chemistry , orthorhombic crystal system , crystal structure , lactone , ring (chemistry) , cyclopentenone , stereochemistry , crystallography , molecule , epoxide , chirality (physics) , hydrogen bond , absolute configuration , organic chemistry , nambu–jona lasinio model , chiral symmetry breaking , physics , quantum mechanics , quark , catalysis
The isolation and structure determination of two new guaianolides, pumilin and its 2,3‐epoxide, from Berlandiera pumila and B. texana are reported. The structure of pumilin was determined from nmr and mass spectral data, and from an X‐ray single crystal study; the structure of the epoxide was found by comparison of nmr spectra. Pumilin is shown to be a Δ 1(10) ‐ cis ‐guaianolide with a cyclopentenone ring attached to C1 and C5, and an α‐methylene‐γ‐lactone ring trans ‐fused to C6 and C7. The absolute configuration was inferred from spectral considerations and knowledge of previous structural determinations. The cd spectrum of pumilin exhibits a negative Cotton effect, and the lactone chromophore has left‐handed chirality. The cyclo‐heptene ring is in the chair configuration, with the lactone a half‐chair and the cyclopentenone essentially planar. Crystals are orthorhombic, a = 7.065, b = 13.652, c = 19.586 Å, space group P2 1 2 1 2 1 , Z = 4, and the final R value is 3.9%. The crystal structure is strengthened by an O···O hydrogen bond linking the molecules into infinite chains.