Additivity relations in carbon-13 nuclear magnetic resonance spectra of dihydroxy steroids

Abstract

The I3C NMR spectra of 26 dihydroxy steroids and 10 acetylated derivatives have been obtained and assigned.It was found that only for compounds with 1,2or 1,3-dihydroxy groups are there significant differences between the observed chemical shifts and those calculated assuming additivity of the substituent effects found for the monosubstituted compounds. When there is steric interaction between the functionalities the deviation from additivity can be rationalized by considering the nature of the steric interactions which are introduced. It is demonstrated that in many cases the effect of OH-OH interactions can be approximated by the magnitude and direction of analogous OH-C or C-C interactions. Significant deviations from additivity were also found for a few compounds with no steric interaction between the substituents (1,3-trans and 1,e-diaxial diols). An upfield 1,3-syn-diaxial6 substituent effect is reported.

Isolation of 20 Glycosides from the StarfishHenriciadowneyae, Collected in the Gulf of Mexico

“…The small shifts observed in the 13 C NMR spectrum of 11 for C-14 (γ effect) and for C-17 (β effect) relative to thornasterol A [i.e., 3β,6R-dihydroxy-5Rcholest-9(11)-en-20-one) 9 (i.e., -1.0 and +1.1 ppm, respectively] are also consistent with a 16β-hydroxy substitution. 28,29 Therefore, on the basis of the above results, downeyoside K has structure 11, that is (20S)-3β-O-(β-glucuronopyranosyl)-6β,20-dihydroxy-5R-cholest-9(11)-en-6R-yl sulfate. Downeyoside L (12), FABMS m/z 713 [MNaSO 3 ] -, 691 [MHSO 3 ] -, 515 [713 -sodium glucuronate] -is the 9(11)-dihydro derivative of 11, as conclusively shown by its NMR spectra (Experimental Section) and comparison with those of downeyoside K (11).…”

Starfish Saponins, Part 49. New Cytotoxic Steroidal Glycosides from the Starfish Fromia monilis

“…In the 13C-nmrit gives rise to a decreased shielding -gauche effect at C-l 1 (-2.1 ppm) relative to that expected (12) and to equally unexpected deshielding effects at the -carbons C-6 (+1.8 ppm) and C-l5 (+0.7 ppm). The large deviations from additivity must be associated with skeletal deformations taking place to relieve the severe steric hindrance caused by the 1,3 syn-diaxial interactions suffered by the ß-hydroxyl with C-18 and C-19 methyl groups and with 6ß-and 15ß-^ 1 groups (13).…”

Unusual withanolides from aeroponically grown Withania somnifera

“…The signals due to the withanolide moiety of the 13 C NMR spectrum of this compound were similar to those reported for 3b-ethoxywithaferin A (Pelletier et al, 1979) suggesting that the n-butyloxy moiety is attached to C-3 of the withanolide. Comparison of the chemical shifts of C-3 of compound 3 (d 77.6) with that reported for C-3 of 3b-ethoxywithaferin A (d 77.5) (Pelletier et al, 1979) suggested b-orientation of the nbutyloxy moiety at C-3 (VanAntwerp et al, 1977). This compound was thus identified as 3b-O-butyl-2,3-dihydrowithaferin A (3).…”