Stereochemistry of some Altersolanol B Derivatives and their Correlation with Bostrycin

Abstract

The results of a complete analysis of the proton spectra of altersolanol B acetonide indicate that this compound exists preferentially in the half-chair conformation corresponding to that favored by the parent pigment in the solid state, as shown by previous X-ray studies. In contrast, the triacetate derivative apparently adopts the alternative half-chair conformation.Les rtsultats d'une analyse compltte r.m.n. de l'altersolanol B acttonide indique que ce compost existe prtftrentiellement sous la forme demi-chaise correspondant a celle favoriste par le pigment de base dans I'ttat solide, comme l'ont montr6 de prictdentes etudes rayons-X. En revanche, le dtrivt triacttate adopte apparemment la conformation demi-chaise alternative.Canadian Journal of Chemistry, 50, 122 (1972) In an earlier paper on some metabolites of Alternaria solani (I), structures were proposed for altersolanol B (1, R = R' = H), its triacetate (1, R = R' = Ac) and isopropylidene (2) derivatives. To confirm the assigned structures and to obtain information bearing on the probable conformations of these materials, a complete analysis of the proton spectrum of acetonide 2 was undertaken. In the interim Noda et al. (2) reported the results of their structural study of bostrycin (3), a closely related tetrahydroanthraquinone pigment. These authors found that treatment of hydrogenation products of 3 with p-bromobenzoyl chloride in pyridine yielded a crystalline ester which was subsequently hydrolyzed in these laboratories to give altersolanol B as judged by t.1.c. and U.V. spectra. X-Ray diffraction results for the p-bromobenzoate 1 (R = H, R' = p-BrC,H,CO) were presented by Takenaka et al. (3). As a further check on the correspondence between the two pigments a sample of acetonide 2 was treated with p-bromobenzoic anhydride in tetrahydrofuran containing some y-dimethylaminopyridine to yield an acetonide ester. Upon removal of the isopropylidene group, the resulting p-bromobenzoate was compared to an authentic sample of the degradation product obtained by Noda et al. mixture m.p., i.r. and U.V. spectra and specific rotation. Consequently, the structures originally proposed are undoubtedly correct but the question of preferred conformation remained.In addition to the methyl proton absorptions, the high field region of the proton spectrum of 2 consists of two overlapping AB patterns one of which is part of an ABX system; since the two AB patterns are long-range coupled a better description of the spin system may be ABMNX. To Can. J. Chem. Downloaded from www.nrcresearchpress.com by 34.214.212.150 on 05/11/18For personal use only.

The Complete Stereostructure of Capsidiol. X-Ray Analysis and 13C Nuclear Magnetic Resonance of Eremophilane Derivatives Having trans-Vicinal Methyl Groups

“…With the exception of epicapsidiol (3), the capsidiol derivatives have been described previously (1). The model compounds included in this study were known materials but slightly modified preparations for 10 and 16 are described below.…”

“…A n additional flattening may have been expected as a result of the presence of three axial substituents. From an electron diffraction study of 1, determined an average endocyclic torsional angle of 51.7" and they attributed the flattening priCan. J. Chem.…”

“…Nevertheless, it appears that the angle at C-5 is smaller than normal while that at C-6 is larger than normal. The abnormally small angles C(2)-C(1)-O (1) and C(6)-C(5)-C(15) are further manifestations of the repulsion between the two syn-axial substituents. Similarly, the angle C(5)-C(4)-C (14) indicates that C-14 is bent away from ring B, thus increasing its distance to C-7 to 3.257(4) A. There are two intermolecular hydrogen bonds in the crystal structure (Table 5).…”

“…Chem., 52,993 (1974) The gross structure of capsidiol (1) and of C-10. Since alternative conformations for 1 could several derivatives (2, 6 6 ) had been determined not be rigorously excluded with the available and, as described in the earlier report (1), the pro-data, conclusive evidence was sought from a deton spectral data indicated that this series of anti-tailed analysis of the 13C spectra of this series of fungal sesquiterpenes differed from all previously compounds. It is well established that the shielddescribed eremophilanes in that the vicinal methyl groups (C-14 and -15) are in a trans disposition.…”

Absolute stereochemistry of altersolanol a and alterporriols

“…14 The full structure of bostrycin had been established with X-ray crystallographic analysis after some derivatizations. 15 The absolute stereochemistry was confirmed by CD in a more deductive manner (Scheme 2).…”