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The absolute configuration of the 2-(phenylmethyl) pyridine derivatives 1-9 had been established by X-ray diffraction and chemical correlation. Their CD spectra have been studied in different solvents for the free and protonated forms. It has now been found that, from the sign of the strong CD couplet between 270 and 220 nm, which was observable for all these compounds besides 7 and 9, their absolute configuration can be determined much quicker

The chiroptical properties of the C(5)-epimeric 4,4-dimethyl-steroidderivatives 6, 7 and 8, recently prepared [1], are reported.

The absolute configurations of (+)-cantharic acid, a chiral derivative of the achiral insect defensive substance cantharidin (1), and of palasonin, a lower homologue of 1 occurring in the plant Butea frondosa, were shown to be represented by formulas 2 and 3, respectively (scheme 1). These results were obtained by application of the Horeau method (table 1) on the (+)-cantharic acid derivatives (+)-5, (−)-7, and (−) 11 (scheme 2), and the palasonin derivatives (+)-29 and (+)-30 (scheme 4), as well as by comparison of the chiroptical properties (tables 2 and 3) of a number of derivatives, prepared from either cantharic acid or palasonin. – Attempts to incorporate various radioactively labelled precursors into palasonin (3), using young and adult plants, have been so far unsuccessful.

The absolute configuration of dechlorogilmaniellin (2) could be determined from its chiroptical data by applying coupled-oscillator theory to the CD couplet around 272 nm and from the sign of its n π*Cotton effect. Gilmaniellin (1) has the same absolute configuration.

Hydrogenation of the ketone group in di-O-benzylderivative (8) of the known macrocyclic lactone zeralenone (7) using a novel chiral borane complex 3. BH3, prepared in situ, proceeded at lower temperatures with moderate diastereoselectivity (∼40%, d. e. at −60°). Unsaturated diastereomers 9 and 10 were separated, and 9 converted into zeranol (11), a known anabolic agent. Restricted conformational mobility at lower temperatures is assumed for the intermediate 8 on the basis of the temperature-dependent CD spectra of its acetyl congeners 18 and 19. X-Ray structure analysis of 7-O-acetylderivative (13) of 11 revealed the (R)-configuration at C(7). Two crystallographically independent H2O molecules are involved in the H-bonds, one of them (O(21)) rises the helices of the molecules of 13 along b. Small positive torsional angle [C(16)-]C(161)-C(1) [=O] (+19.3°), transoid(E) conformation of the lactone group, and nearly achiral arrangement of the C(11)-C(12) bond (torsional angle [C(11)-]C(12)-C(121)[C(161)] is −93°) are the main conformational features that differentiate the macrocylic RAL (resorcinic-acid lactone) derivatives from the 6-membered lactone derivative 20, studied earlier by CD. Consequently, the rules developed for the CD effects within conjugation band (around 270 nm), and nπ* band (around 255 nm) of the latter compound, cannot be applied the macrocyclic lactones.

The circular dichroism of keto derivatives with trichothecane skeleton and some of their rearrangement products has been measured. The sign (and sometimes even the magnitude) of all COTTON effects can be explained by applying the respective rules for the cyclohexanone, cyclopentanone, enone and ene-ester chromophores. Thus conformations could also be determined in those cases which did not follow unambiguously from conformational analysis. The conformation of the muconic acid moiety of the macrocyclic ring of verrucarin A is the same in dioxane solution as in the crystalline state.

– The circular dichroism of some non-conjugated unsaturated carbonyl compounds, which are conformationally mobile, has been measured at +20° and at about −178°. Specifically for the steroidal compounds 1 and 2 and the monocyclic aldehyde 14, their substituted analogs 4–6, 9–11, and 15–19, respectively, as well as for the aliphatic ketone 21 the CD. temperature gradients are interpreted in terms of the preferred conformations. In the case of the β,γ-unsaturated aldehydes 1 and 14, a correlation of these results with the photolytic decarbonylation from the excited singlet states is discussed.

The absolute configuration of (+)-α-ionone 3 (R), the absolute configurations at C(6) of (+)-cis-α-irone 5 (6S) and (−)-trans-α-irone 6 (6R), and the absolute configurations of (+)-cis-abscisic acid 10 (S) and (+)-trans-abscisic acid 11 (S) are deduced from the CD.-spectra.

The circular dichroism (CD) of saturated and α,β-unsaturated ketones containing three-membered rings has been measured and correlated with the configurations and conformations of these compounds.

The Circular Dichroism (CD.) of several saturated and conjugated keto-A-nor-steroids follows the known rules. Homochiral α,β-epoxy-cyclopentanones and -cyclohexanones give the same sign of the Cotton effect within the R-band, whereas the K-band CD. of the former has opposite sign to that at 300 nm. More examples for the application of the rule for the determination of the CD. of non-coplanar conjugated lactones as well as α,β-epoxy-lactones are presented.

The structure of panepoxydone (1) and some related products, produced by two species of Panus (basidiomycetes), are proposed on the basis of chemical transformations and physical measurements. The absolute configurations of the main products are deduced by the interpretation of CD. studies and compared with those of the structurally related compounds epoxydone (10), terreic acid (11) and terremutin (12).

The structure of carquejol is amended to that of cis-3-hydroxy-o-mentha-1(7),4,8-triene; the chirality has been confirmed as 2 R, 3 S by correlation with the (−)-cis-o-menthane obtained from carquejol and that from (+)-verbenene of known absolute configuration. The two double bonds of the dihydrocarquejol system (15 and 16) constitute a helical system, that especially in the case of the acetate (16) fixes the isopropenyl group in such a way that a very high Δϵ value in the CD. curve is observed. The conformational significance of this phenomenon is discussed.