Preparation of Steroid Structural Data for the Consideration of Possible Structural-Functional Relationships

Abstract

A format has been established for the presentation of steroid structural data which may prove to be useful in the consideration of the possible structural-functional relationships of steroids in biological systems. In preparing this format the detailed structural information for all steroids with known crystallographic structures has been computed and summarized, including bond lengths and angles, non-planarity coefficients, dihedral angles, length of the steroid nucleus, and side group inclinations. From the structural point of view it is interesting to note that (a) bond lengths do not differ significantly from the theoretical values, (b) bond angles do differ significantly from the theoretical values, (c) the non-planarity coefficient of the steroid molecule seems to be a function of the number of angular methyl groups but is unaffected by the presence of one heavy atom, (d) except where aromatic bonds are present the non-planarity coefficients of the two-ring and one-ring subdivisions of the steroid nucleus is 0.25 A, (e) the average non-planarity coefficient of the ring joins and "seat" portions of the chairs is 0.03 A, (f) dihedral angles deviate from the theoretically expected values and also show wide variation in the steroids studied, (g) the length of the steroid nucleus is variable, (h) analysis of side group inclination data must be deferred until more steroid structural information is available. From the biological point of view it is currently impossible to estimate the importance of each steroid structural feature in determining physiological function.

The structure of Δ-8,l4-anhydrodigitoxigenin, C23H32O3, by direct phase determination

“…The folded nucleus of DTG is significantly shorter, 7.25 A, than that of ADTG, 8.44 A. A detailed discussion of the conformations of six steroids has been published (Norton, 1965) in which the steroid nuclei contained only trans ring junctions and therefore were relatively planar. Their C(3).-.C(16) distances, 9.1 + 0-2 A, were necessarily longer than those reported here.…”