The uCNMR spectra of 29 highly oxygenated C , steroids with the withanolide skeleton, 24 of which are naturally occurring substances or acetates thereof, were recorded and the carbon signals fully assigned. The shifts of the heavily functionalized A/B ring system can serve as a '6ngerprint' for the di5erent substitution patterns. A study of the e5ects of hydroxyl substitution in the ring D/side chain part of the molecules leads to conformational information, including preferred rotamers around the 17-20 and 20-22 bonds. Systems with both 17a-and 17p-oriented side chains are thus analysed.The study of l3CNMR data and their applications in structural and conformational analyses in the area of naturally occurring substances, including steroids,' has grown enormously in the past decade. However, very has been reported for the important family of heavily oxygenated steroidal lactones known as the withanolide~.~ As a continuation of our interest in these and related substances it became necessary to rely on a basic investigation of their 13CNMR spectroscopy; this work represents the result of such a study and its implications in the conformational analysis of these molecules. The data presented below have already proved useful in the structure elucidation of related corn pound^^-^ and led, in a few cases, to the revision of previously accepted formulae.lO-'l EXPERIMENTALThe 13CNMR spectra were recorded on a Bruker WH-90 spectrometer operating at 22.63 MHz in the Fourier transform mode. Spectral widths of 4200 Hz and the use of 8 K data points resulted in acquisition times (and pulse delays) of 0.974s and in a digital resolution of k0.05ppm. The pulse widths used correspond to flip angles of 45-60'.All reported chemical shifts are in ppm downfield from internal TMS, for solutions in CDCl,. In some cases, as mentioned in the Tables, up to 15% of methanol was necessary to improve sample solubility. For a few compounds spectra were run with and without methanol in order to determine the solvent effect. There is a small (up to 0.4ppm depending on the amount of methanol) downfield shift of all the carbons (probably a real upfield shift of the TMS reference) relative to the spectrum in pure CDCl,, accompanied by unimportant (no more than k0.2 ppm) additional changes. Exceptions to this are the carbonyls and 6-carbons of the a$-unsaturated carbonyl moieties (which are shifted downfield by 1-2 ppm due to hydrogen bonding to the hydroxylic * Author to whom correspondence should be addressed. solvent), as well as other oxygenated or sp2-hybridized carbons (which shift by up to k0.7ppm, without apparent regularity).Concentrations of 100 mg ml-l were used when possible, but these were sometimes limited by sample availability to as low as 15 mgml-l. Spectra were taken at normal probe temperature (29k2 "C).The 3J Original references to most of the substances studied can be found in a review a r t i~l e .~ However, all the compounds described in the review as having an 8,14 double bond were found to possess, in reality, a 14a-OH funct...
1709 and 1695 cm-l. These data suggest two apunsaturated carbonyl systems in (IV), the double bond of one being easily reduced (IV) +-(XII). This information could be completed by inspection of the n.m.r. spectrum of (IV). In the low-field region there are two signals for vinylic hydrogens at 6 5.81 and 6.60 p.p.m. which, according to their position and * Withanone, a compound of unknown structure isolated from Withania somnifera (collected in India, Delhi area) 5a has been found to be identical with compound (IV) 66.
No abstract
The Structure of the products obtained by treatment of (1 7S,20S,22R)-5~,6~-epoxy-l4a,l7,20-trihydroxy-loxowitha-2,24-dienolide (withanolide E) with sulphuric acid in acetone solution has been reinvestigated. Whereas the major component is indeed (1 7S,20S,22R) -5a,6P,17,20-tetrahydroxy-l -oxowitha-2,14,24-trienolide, the minor component which was previously considered to be the isomer of the latter, has now been shown to be (1 7S,22R),14a,20~-epoxy-5a,6~,17-trihydroxy-l-oxowitha-2,24-diendide. The configuration a t C-20 is most probably 20R.PREVIOUSLY we reported the chemical work done for the characterization of (17S,2OS,22R)-5p,6p-epoxy-l4a,-1 7 , 20-trih ydroxy-1 -oxowitha-2,24-dienolide (wit hanolide
Four related steroidal lactones of the withanolide group possessing a 1 7a-oriented side chain have been characterised as (1 7S.20S.22R) -5~,6~-epoxy-l4a,l7,20-trihydroxy-l -oxowitha-2,24-dienolide [withanolide E (1 )],(1 7S,20S.22R)-14a,l7,20-trihydroxy-l -oxowitha-2.5.24-trienolide [withanolide F (2)], (1 7S,20S,22R)-5a,6P,-14a.17.20-pentahydroxy-1 -oxowitha-2.24-dienolide [withanolide S (3)], and (1 7R,20R,22R)-14a,17-dihydroxy-1 -oxowitha-2.5.24-trienolide [withanolide P (4)]. The structure of withanolide E'deduced here has been confirmed by X-ray analysis (reported elsewhere) ; those of withanolide F and S are related to that of withanolide E on the basis of common degradation products. The identification of withanolide P is based on spectral analysis. Rehovot, IsraelWE have briefly reported the isolation of withanolides E (1) and F (2), two steroidal lactones of the withanolide group, characterised by the unusual a-orientation of the side chain.1 The structure of withanolide E (1) was unequivocally determined by crystallographic analysis,l as (1 7S,20S,22R) -5 p,6@-epoxy-14a, 17,20-trihydroxy-1oxowitha-2,24-dienolide , with a boat-like conformation for ring A, a distorted half chair for ring B, and a normal chair for ring c; ring D has an envelope form in which C( 14) is out-of-plane. The compound crystallises with two molecules of water; the C( 14) and C(20) hydroxygroups are hydrogen bonded. As a result, the 17p-OH . C(13)Me and 17p-OH . '22-H distances are decreased, and the 20a-OH --C(13)Me distance is
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