Two‐dimensional NMR studies of cyperene

Abstract

Combined utilization of 'H-IH homonuclear and 'H-l'C heteronuclear N M R chemical shift correlations,two-dimensional J-resolved 'H NMR measurements and homonuclear 'H double resonance experiments allowed specific assignments for both 'H and -C NMR frequencies to be made for the tricyclic sesquiterpene cyperene. The results also provided information on the conformation of the six-membered ring of this natural product, which was recognized as a distorted chair.Cyperene (1) is a tricyclic monounsaturated hydrocarbon of pleasant odour originally isolated from Cyperus1 and, more recently, from Perezia.' Its structure is closely related to that of a -and y-patch~ulenes,'~~ constituents of the fine perfume of patchouli the only difference being the position of the double bond, which is located6 between carbons 4 and 5 in CYpatchoulene and as an exocyclic methylene group at C-4 in y-patchoulene. Two other related molecules, @-and 6 -p a t~h o u l e n e ,~~~ have the 4,7-methanoazulene skeleton"' instead of the 3a,7-methanoazulene framework present in cyperene (1) and in a -and y -patchoulenes. Owing to the close structural relationship of cyperene to the highly expensive and widely appreciated patchoulenes, and the fact that cyperene analogues have already been found as minor constituents in plant m a t e r i a l~, l "~~~-~~ it seemed desirable to undertake detailed NMR studies of the more easily accessible cyperene. These studies might be of further utility for the structural elucidation of other closely related natural products. RESULTS ~The detailed assignment of both the 'H and I3C NMR spectra of cyperene is difficult since, on the one hand, the twelve 'H methylene and methine signals are found between 1.1 and 2.7ppm and, on the other, in the 13C spectrum four methylene signals appear within a range of only 2ppm. Further, since three of these methylene signals are within a very narrow range of only 0.82 ppm, and sp3-sp3 one-bond carbon-carbon coupling constants are of the orderc6 of 35 Hz, the use * Authors to whom correspondence should be addressed.of double quantum coherence17 measurements is not recommended since, in such cases,l* strongly coupled AB systems with distorted intensities arise.Therefore, the 'H and 13C spectral parameters for cyperene were deduced from both heteronuclearl' (lH-13C) and homonuclear2' (lH-lH) chemical shift correlations, and several coupling constants were obtained from the homonuclear J-resolved'l 'H NMR spectrum and from one-dimensional 'H measurements with the aid of spin-spin decoupling experiments, which also provide information on the conformation of the six-membered ring of the natural product 1.Preliminary information about the number of directly attached protons to each sp3 carbon atom was obtained from two APT (attached proton test) experi-

Norsesquiterpene hydrocarbon, chemical composition and antimicrobial activity of Rhaponticum carthamoides root essential oil

“…1) was confirmed by structural analysis on GC-MS, GC-FTIR and comparison with described 13 C NMR data (Joseph-Nathan et al, 1984). The use of homo-and heteronuclear 2D-NMR spectra allowed us to make also complete structural assignment of proton signals in CDCl 3 ( Table 2).…”

Diterpenoids from the roots of Croton dichogamus Pax

“…The n-hexane, CH 2 Cl 2 and MeOH extracts of the root of Croton dichogamus were separated using flash chromatography followed by preparative thin layer chromatography and/or gravity column chromatography to yield five previously unreported (2, 3, 5, 6, and 19) and 15 known compounds. The known compounds were identified from their spectroscopic data and by comparison against literature data, as crotohaumanoxide (1) previously isolated from Croton haumanianus (Tchissambou et al, 1990), depressin (4), a casbain diterpenoid previously isolated from the soft coral Sinularia depressa (Li et al, 2010), 15,16-epoxy-3α,4β-dihydroxy-13(16),14-ent-clerodadien-17,(12S)-olide (furocrotinsulolide A) 7previously isolated from Croton insularis (Graikou et al, 2005), 15,16-epoxy-3-keto-13(16),14-ent-clerodadien-17,(12S)-olide (crotonolide E) (8) and 15,16-epoxy-3α-hydroxy-4(18),13(16),14-ent-clerodatrien-17,(12S)-olide (crotonolide F) (9) previously isolated from Croton laui (Liu et at., 2014), 3β,4β,15,16-diepoxy-13(16),14-ent-clerodadiene-17,(12S)olide (10) previously isolated from Croton oblongifolius (Pudhom and Sommit;2011), 15,16epoxy-4(18),13(16),14-ent-clerodatrien-3α-ol (gbaninol) (11), 15,16-epoxy-13(16),14-entclerodadien-3-one (trans-cascarillone) (12) previously isolated from Croton sonderianus (McChesny and Silveira, 1990), 3β,4β,15,16-diepoxy-13(16),14-clerodadiene (13) previously isolated from Thysananthus spathulistipus (Harinantenaina et al, 2006), 4-patchoulene (cyperene) (14) and 4-patchoulen-3-one (cyperotundone) (15) previously isolated from Cyperus rotundus (Joseph-Nathan et al, 1984;Xu et al, 2009), 6α-methoxypatchoulan-4-ene (16) previously isolated from Croton muscicapa (Barreto et al, 2013), 4-isopropyl-1,6dimethylnaphthalene (cadalene) (17) previously isolated from Siparuna macrotepala (El-Seedi, 1994), 1(6),7,9-cadinatriene-4α,5β-diol (4α,5β-corocalanediol) (18) previously isolated from Juniperus formosana (Kuo et al, 1990), and aleuritolic acid (20) previously isolated from many sources, including C. pseudopulchellus (Langat et al, 2012). The structures of the patchoulenes (14-16) were determined with the assistance of the NMR Predict programme (Robien, 2014).…”

Germacrene A–A Central Intermediate in Sesquiterpene Biosynthesis

“…The (−)‐enantiomer of 138 was later isolated from several other plants [177, 349, 354–367] . Full 1 H‐ and 13 C‐NMR data in CDCl 3 and C 6 D 6 have been reported [367, 368] …”

“…[177,349,[354][355][356][357][358][359][360][361][362][363][364][365][366][367] Full 1 H-and 13 C-NMRd ata in CDCl 3 and C 6 D 6 have been reported. [367,368]…”