¹³C n.m.r. spectra of steroids —a survey and commentary

Abstract

The literature on "C n.m.r. examinations of steroids has been reviewed and the shielding data for over 400 examples are tabulated. The assignments for each compound have been-ionsidered and, where necessary, revised in the light of more recent evidence and for consistency throughout each series. The methods available for assignments are reviewed and, in many cases, illustrated with specific examples. The major practical features concerning "C studies of steroids are discussed as a guide to the use of the technique. From the main body of shielding data, an extensive set of substituent effects has been generated to aid the examination of new systems. The ntility and the limitations of these effects are described.Since the iirst report in 1969 b] Roberts's group' clearly established the utility of C n.m.r. studies of steroids, more than fifty papers have appeared extending the original work. A key factor in the development of this field has been the advent of n.m.r. instrumentation which permits the routine acquisition of 13C shielding data. Some of these papers have provided compilations of some have examined substituent effects in the steroid f r a m e w~r k , '~-~~' 29-32 others have used 13C n.m.r. data to support or provide a stereochemical assignment or structural identification,3346 while a few have used the 13C data to derive information on mechanistic roblemsZ8 and complexation behavior of It seems an appropriate time to review the available data, to compile the shieldings for the steroids which have been examined, and to revise those assignments which more recent results indicate are in error. Included in this compilation are the previously unpublished data for more than fifty cholestanes, androstanes and pregnanes. The trends exhibited by the results are also considered in an alternative format by way of a table of substituent cffects. These effects are particularly useful for predictive purposes. The methods which have been used to make assignments of the signals in the steroid spectra are discussed and illustrated. Previous reviews and compilations of 13C n.m.r. spectra of more limited ranges of steroids have appeared.49ps0'79In this review, we have subdivided the discussion into four major sections. First, a general description of experimental methods and techniques for obtaining steroid spectra is presented and then the variety of approaches for making specific signal assignments is considered, with examples drawn fiom the main data compilation. In the third section the shielding results are discussed, particularly with regard to the assign-B

Reactions of steroidal 5,6-epoxides and cyclohexene oxide with aluminum alkoxides

“…The structures of 9 and 10 follow from their I3C nmr spectra (Table 2). Chemical shifts diagnostic of stereochemistry are those of C-19 (for 5P steroids), C-1 and C-5 (for C-3 alcohols), and C-4 and C-8 (for C-6 alcohols) (13). The 'H nmr spectra of 9 and 10 (see Experimental), in particular the multiplicity of the signal assigned to the C-6 hydrogen, support the structural assignments.…”

“…The residue was chromatographed using benzene to ether elution (10% step gradient) to give, in order of elution, a mixture of cholesta-3,s-diene (3) and cholesta-4,6-diene (4) (0.145 g), mp 78-80°C, identified by 'H and I3C nmr comparison with the spectra of the authentic separated isomers (10); cholestane-5a,6P-dio1 (5 3,4-secocholest-4-ene-3,6a-diol (8) (0.06 g) Table 2; SP-cholestane-3a,6P-diol (9b) (0.03 g), mp 148-150°C (lit. (21) mp 142-143.S°C), 'H nmr included signals at 6 3.4-3.85 (lH, br m, C-3P H) and 3.75 (lH, br s, Wl12 = 5 Hz, C-6a H) ppm; I3C nmr, see Table 2; SP-cholestane-3P,6a-diol(lOa) (0.016 g), mp 212-215°C; IH nmr included signals at 6 3.35-3.75 (lH, br m, C-3a H) and 4.10 (lH, br s, Wl12 = 12 Hz, C-6P H); 13 C nmr, see Table 2. Anal.…”

“…calcd. for C21H4802: C 80.14, H 1 1.95%; found: C 80.04, H 11.74%; and SP-cholestane-3a,6a-diol (9a) (0.024 g), mp 167-170°C; IH nmr included signals at 6 3.4-3.9 (lH, br m, C-3P H) and 3.95 and 4.08 (lH, dd, J = 4 , 9 Hz, C-6P H) ppm; 13 C nmr, see Table 2. Anal.…”

“…In view of the complexity of the reactions observed between the steroidal epoxides and aluminum isopropoxide, we decided to investigate reaction of the latter with the simple epoxide, cyclohexene oxide (13). Two products were isolated and identified by their spectral characteristics as isomers of a substituted dicyclohexyl ether.…”

Chemical constituents of Simarouba versicolor

“…The presence of steroids 15-17 in a mixture was mainly deduced by 13 C NMR spectral data, which involved comparison with values reported in the literature (Blunt andStother 1977, Chaurasia andWichtl 1987) The flavonol kaempferol (18) obtained as its acetyl derivative (18a) (Arriaga et al 1994) is frequently isolated of plants.…”