¹³C-nmr Studies of Cedranolides

Abstract

hsTRAcT.-The assignment of the 13C-nmr spectra of several naturally occurring cedranolides, which include the highly oxygenated perezols (lb, 2b, and IC) and pipitzols (laand 2a), was completed. For this purpose, it was necessary to prepare a large body of derivatives, many of them regiospecifically labeled with deuterium atoms at several positions. The data are self-consistent and provide a base for the study ofother tricyclic sesquiterpenes belonging to the 3,6,8,8-tetramethyl-3a,7-methanoperhydroulene group.The naturally occurring cedranolides comprise a group of sesquiterpenes possessing the 3,6,8,8-tetramethyl-3a,7-methanoperhydroazulene skeleton. Among these, a-(la) and p-pipittol(2a), isolated from Perezza cuernavarana (1-3), as well as cedrol (4,5) and cedrene (loa> (4,6,7), constituents of cedar oil, have received considerable attention.Although cedrol and a-cedrene (loa) have been the subjects of several 13C analyses (8-12), there is, to our knowledge, no systematic discussion concerning an array of 13C-chemical shift data on cedrane derivatives. A 13C analysis of a series of these structurally complex molecules may be of great utility in the characterization of natural products possessing similar structures, such as 6,12-epoxycedrane ( 1 3 , 6,12-cedranolide ( 1 3 , bs, 12-cedranediol (13), cedrolic acid ( 1 3 , a-biotol (14), p-biotol (14), 5,6-cedranediol(15), 5-cedren-13-01(13), and juniper01 (16).From a preliminary inspection of the structure of these complex molecules, it seems evident that specific assignments of all signals might be complicated in the molecular framework due to its rigidity, which is associated with some steric factors. Thus, in order to achieve secure spectral assignments, it was necessary to resort to the preparation of a series of cedrane derivatives, some of them labeled with deuterium atoms at specific positions.The present work describes the 13C-spectral analysis of a series of cedranolides that includes derivatives of the naturally occurring a-(la) and p-pipitzol(2a); a-(lb), p-(2b) and y-perezol (IC); 5-isocedranone (7a) and 5-cedranone (13a), in which the as-0 R ' I 0 R' I I I la R~= H , R~= H 2a R'=H, R 2 = 0 , R 3 = 0 , R4=H Ib R'=H, R'=OAngelate 2b R'=H, R 2 = 0 , R 3 = 0 , R4=OAngelate IC R'=H, R~= O H 2c R'=Me, R 2 = 0 , R 3 = 0 , R4=H Id R'=Me, R 2 = H 2d R'=Bz, R 2 = 0 , R 3 = 0 , R4=H le R ' = B~, R~= H 2e R'=Bz, R2=H,, R 3 = 0 , R4=H 2f R'=Bz, R2=H,, R3=H2, R4=H 'Present address: Instituto de Investigaciones Quimico Biologicas, Universidad Michoacana de San Nicolh de Hidalgo, Morelia, Mich. 58240 MCxico.

Vibrational Circular Dichroism Discrimination of Diastereomeric Cedranol Acetates

“…Cedranol acetates 1 , 2 , 3 , 4 are tricyclic sesquiterpene derivatives which belong to a naturally occurring family with the (3 R ,3a R ,7 S ,8a S )‐3,6,8,8‐tetramethyl‐3a,7‐methanoperhydroazulene skeleton, whose relative stereochemistry at C5 and C6 has been established by 1 H and 13 C NMR . Diastereomers 1 , 2 , 3 , 4 have molecular formula C 17 H 28 O 2 , with 19 heavy atoms, 146 electrons, and 135 vibrational frequency modes that are active vibrations in the IR and VCD spectra.…”

“…(−)‐Cedranol acetate 1 , (−)‐neoisocedranol acetate 2 , (−)‐neocedranol acetate 3 , and (+)‐isocedranol acetate 4 were obtained by acetylation of their corresponding alcohols, which, in turn, were obtained from (3 R ,3a R ,7 S ,8a S ) (−)cedrene . The IR and VCD measurements were performed on a BioTools‐BOMEM Chiral IR FT‐VCD spectrophotometer equipped with dual photoelastic modulation.…”

Acetyl cedrene and its follower. An Isotopic, NMR and MS Structure elucidation and deuteriation study

“…It is also seen that the peak in the chromatogram at 8.916 (cuparene according the NIST database) is left unaltered, whereas the peak at 8.817 (ascribed to 1,1,8,9a, tetramethyl-2,3,5,6,7,9a-hexahydro-1H-benzo [7]annulene by the NIST data base) disappears upon acetylation, but not leading to the follower. Formation of the follower requires an acetylation followed probably by ring extension and extensive rearrangements and loss of a water molecule.…”

“…The Virginia type contains different cedrenes, thujopsene and cuparene (Figure 3(a)). The one from Urtegaarden contains none of these products, but rearrangement products such as 3,5,5-trimethyl-9-methylene-2,4a,5,6,7,8,9,9a-octahydro-1H-benzo [7]annulene, and 1,4-1,2,3,3a,4,5,6,8a-octahydro-1,5,5,8a-tetramethyl-,(1S,3aR,4S,8aS)-methanoazulene.…”

“…5,6 Specifically deuteriated samples of cedrol and a-cedrene are described. [7][8][9] Acetyl cedrene (1) from Sigma-Aldrich is seen to contain a small impurity, 1,7,7-trimethyl-2,3-(3 0 ,4 0 -dimethylbenzo)bicyclo[3.2.1]octane (2) (Figures 1 and 2 (b)). This impurity is even larger in 1 obtained from IFF (International Flavors and Fragrances).…”