The stereochemistry of pipitzols and perezols

Joseph‐Nathan, Pedro; Román, Luisa U.; Hernández, José Falcón; Taira, Zenei; Watson, W.H.

doi:10.1016/s0040-4020(01)93686-5

Cited by 9 publications

(11 citation statements)

References 8 publications

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“…In turn, the structures of tricyclic natural occurring sesquiterpenes α ‐pipitzol ( 4 ) and β ‐pipitzol ( 5 ) followed after extensive chemical degradation reactions, which allowed determining the structure of perezone ( 1 ), whereas their absolute configuration was established by optical rotatory dispersion measurements . In addition, a single crystal X‐ray diffraction study independently confirmed the structure of α ‐pipitzol ( 4 ) and related molecules . Variable temperature 13 C NMR measurements allowed to evaluate the fast interconversion of the two isoenergetic tautomers of 6‐hydroxyperezone ( 3 ), which only could be slowed in the solid state as evidenced by CP‐MAS measurements …”

Section: Introductionmentioning

confidence: 99%

“…[12] In addition, a single crystal X-ray diffraction study independently confirmed the structure of a-pipitzol (4) and related molecules. [13] Variable temperature 13 C NMR measurements [14] allowed to evaluate the fast interconversion of the two isoenergetic tautomers of 6-hydroxyperezone (3), which only could be slowed in the solid state as evidenced by CP-MAS measurements. [15] A few years ago, a conformational study substantiated on NOE and cyclic voltammetry experiments [16] described the side chain of 1 adopts a folded conformation dominated by p-p interactions between the side chain double bond and the quinone system.…”

Section: Introductionmentioning

confidence: 99%

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NMR‐based conformational analysis of perezone and analogues

Zepeda

Burgueño‐Tapia

Pérez‐Hernández

et al. 2013

Magnetic Reson in Chemistry

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Complete assignment of the (1)H NMR chemical shift and coupling constant values of perezone (1), O-methylperezone (2) and 6-hydroxyperezone (3) was carried out by total-line-shape-fitting calculations using the PERCH iterative spectra analysis software (PERCH Solutions Ltd., Kuopio, Finland). The resulting simulated spectra for the three compounds showed strong similarity to their corresponding experimental spectra. Particularly, all vicinal, allylic and homoallylic coupling constant values for the side chain of the three compounds were very similar, thus revealing that the conformation of these three molecules in solution is indeed almost identical. This fact is in agreement with extended side chain conformations over folded chain conformations because 1, 2 and 3 undergo completely different intramolecular cycloaddition reactions. In addition, results of double pulsed field gradient spin echo NOESY 1D experiments performed on perezone (1) were unable to provide evidence for folded conformers.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

NMR‐based conformational analysis of perezone and analogues

Zepeda

Burgueño‐Tapia

Pérez‐Hernández

et al. 2013

Magnetic Reson in Chemistry

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“…A second thioketalization-desulfuration sequence of 4 or 2e afforded the also desired 4,9-¿¿f-desoxo-a-(6a) and 4,9-¿d-desoxo^-pipitzol benzoate (2f), respectively (3).…”

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confidence: 99%

¹³C-nmr Studies of Cedranolides

Joseph‐Nathan¹,

Gutiérrez²,

Hernández³

et al. 1986

J. Nat. Prod.

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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.

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“…Removal of the benzoate residue in 4,9-¿¿r-desoxo^-pipitzol benzoate (15) with KHCOj yielded the corresponding ketone ( 16), the assignment of configuration at C-6 being based on 'H-nmr evidence. It has been described previously (8) that NaHCOj hydrolysis of 4,9-¿¿f-desoxo-ot-pipitzol yields the known 5-isocedranone (14). The structures of 5-isocedranone and ketone 16 keep an enantiomeric relationship, except for the methyl group at C-3, as is evident from the spectral data.…”

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confidence: 67%