Structure of 5 beta-pregnane-3 alpha, 6 alpha, 17 alpha-triol triacetate.

C27H40O7, M(r) = 476.61, monoclinic, P2(1), a = 17.440 (5), b = 13.267 (1), c = 12.168 (2) A, beta = 110.49 (8) degrees, V = 2637.3 (9) A3, Z = 4, Dx = 1.20 g cm-3, lambda (Cu K alpha) = 1.5418 A, mu = 7.04 cm-1, F(000) = 1032, T = 293 K, R = 0.048, wR = 0.068 for 5590 observed reflections with (Fo)2 > 2 sigma [(Fo)2]. The structure contains two crystallographically independent molecules in the asymmetric unit that have almost identical geometry. Rings A, B and C have chair conformations and the D ring assumes a half-chair conformation in both molecules. The progesterone side chain has a conformation typical for other 17 alpha-ester steroids; the C(16)--C(17)--C(20--O(20) torsion angles are -18.2 (5) and -15.0 (4) degrees for the first and the second molecule respectively.

Structure of 6-fluoro-1 beta,2 beta-methylene-3,20-dioxo-9 beta,10 alpha-pregna-4,6-dien-17 alpha-yl acetate.

C24H29FO4, Mr = 400.5, orthorhombic, P2(1)2(1)2(1), a = 12.207 (1), b = 14.715 (1), c = 11.572 (1) A, V = 2078.7 (5) A3, Z = 4, Dx = 1.28 g cm-3, lambda (Cu K alpha) = 1.5418 A, mu = 7.62 cm-1, F(000) = 856, T = 291 K, final R = 0.041 for 2230 observed reflections. The A and B rings assume flat boat and 9 beta,10 alpha-half-chair conformations, with asymmetry parameters delta C3s = 1.5, delta C1,2s = 11.2 and delta C6,7(2) = 3.1, delta C7s = 15.0, respectively.

Structure of 3-hydroxy-17-oxoestra-1,3,5(10)-trien-11 beta-yl acetate.

C20H24O4, Mr = 328.41, orthorhombic, P2(1)2(1)2(1), a = 11.688 (3), b = 15.377 (5), c = 9.466 (2) A, V = 1701 (1) A3, Z = 4, Dx = 1.282 g cm-3, lambda (Mo K alpha) = 0.71073 A, mu = 0.823 cm-1, F(000) = 704, T = 298 K, R = 0.063 for 1921 reflections with F greater than 2 sigma (F). The structure was determined to observe the effect of the 11 beta-acetate substituent on the conformation of the molecule. The 3-hydroxy is hydrogen bonded to O19 at 2.86 A. The B ring has a 7 alpha, 8 beta-half chair conformation, the most commonly observed B ring conformation in estrogen analogues.

Structure of 9 beta-estrone.

3-Hydroxy-9 beta-estra-1,3,5(10)-trien-17-one, C18H22O2, Mr = 270.4, monoclinic, P2(1), a = 9.527 (2), b = 11.182 (3), c = 7.078 (1) A, beta = 108.45 (1) degrees, V = 715.3 (3) A3, Z = 2, Dx = 1.255 g cm-3, lambda (Mo K alpha) = 0.71073 A, mu = 0.746 cm-1, F(000) = 292, T = 298 K, R = 0.037 for 2128 reflections with F greater than 2.0 sigma (F). The compound was one in a series of 9 beta-estrone analogues synthesized to study their estrogenic activity. The B ring conformation is a 7 beta,8 alpha-half chair, due to the configuration at C9. The O3 hydroxy forms a hydrogen bond to O17 at a distance of 2.76 A.

Molecular level model for the agonist/antagonist selectivity of the 1,4-dihydropyridine calcium channel receptor.

Crystal structures of the 1,4-dihydropyridine (1,4-DHP) calcium channel activators Bay K 8643 [methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(3-nitrophenyl)-pyridine-5-carboxy lat e], Bay O 8495 [methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(3-trifluoromethylphenyl)-pyridine-5- carboxylate], and Bay O 9507 [methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(4-nitrophenyl)-pyridine-5-carboxy lat e] were determined. The conformations of the 1,4-DHP rings of these activator analogues of Bay K 8644 [methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyridine-5- carboxylate] do not suggest that their activator properties are as strongly correlated with the degree of 1,4-DHP ring flattening as was indicated for members of the corresponding antagonist series. The solid state hydrogen bonding of the N(1)-H groups of the activators is not, unlike that of their antagonist counterparts, to acceptors that are directly in line with the donor. Rather, acceptor groups are positioned within +/- 60 degrees of the N(1)-H bond in the vertical plane of the 1,4-DHP ring. Previously determined structure-activity relationships have indicated the importance of this N(1)-H group to the activity of the 1,4-DHP antagonists. Based on these observations, a model is advanced to describe the 1,4-DHP binding site of the voltage-gated Ca2+ channel and its ability to accommodate both antagonist and activator ligands.

Structure of 6 beta,6'beta-bi(7 alpha-allyl-3-oxo-4-estren-17 beta-yl acetate).

C46H62O6, Mr = 711.0, orthorhombic, P2(1)2(1)2(1), a = 20.187 (3), b = 22.004 (3), c = 9.180 (1) A, V = 4078 (2) A3, Z = 4, Dx = 1.16 g cm-3, lambda (Mo K alpha) = 0.71069 A, mu = 0.7 cm-1, F(000) = 1544, T = 295 K, R = 0.096 for 3894 unique observed reflections with Fo greater than 2 sigma(Fo). The title compound is a dimer connected by a single bound between C6 and C6' [bond length 1.560 (7) A]. The two steroid moieties are oriented beta-face to beta-face, head to head and lie in almost parallel planes (7.6 degrees), rotated by 45 degrees to one another. The two conformations of the identical portions of the dimer differ chiefly in the orientation of the allyl and acetate groups. C23' (acetate) and O3' form the shortest intermolecular contact less than 3.5 A; C...O = 3.35 (1) A.

Structure of 6 alpha-methylprogesteron-17 alpha-yl pivalate.

C27H40O4, Mr = 428.6, orthorhombic, P2(1)2(1)2(1), a = 9.821(3), b = 25.766(6), c = 9.802(3) A, V = 2480(2) A3, Z = 4, Dx = 1.15 g cm-3, lambda(Mo K alpha) = 0.71073 A, mu = 0.70 cm-1, F(000) = 936, T = 295 K, final R = 0.063 for 2778 observed reflections. The A ring assumes a normal 1 alpha,2 beta-half-chair conformation. The progesterone side chain has a conformation typical of 17 alpha-ester steroids; the C(16)-C(17)-C(20)-O(20) torsion angle is -17.9(5) degrees.

Receptor model for the molecular basis of tissue selectivity of 1, 4-dihydropyridine calcium channel drugs.

Our analysis of the solid state conformations of nifedipine [dimethyl 1,4-dihydro-2,6-dimethyl-4-(2-nitrophenyl)-3,5-pyridinecarboxylate ] and its 1,4-dihydropyridine (1,4-DHP) analogues produced a cartoon description of the important interactions between these drugs and their voltage-dependent calcium channel receptor. In the present study a molecular-level detailed model of the 1,4-DHP receptor binding site has been built from the published amino acid sequence of the alpha 1 subunit of the voltage-dependent calcium channel isolated from rabbit skeletal muscle transverse tubule membranes. The voltage-sensing component of the channel described in this work differs from other reported for the homologous sodium channel in that it incorporates a water structure and a staggered, rather than eclipsed, hydrogen bonded S4 helix conformation. The major recognition surfaces of the receptor lie in helical grooves on the S4 or voltage-sensing alpha-helix that is positioned in the center of the bundle of transmembrane helices that define each of the four calcium channel domains. Multiple binding clefts defined by Arg-X-X-Arg-P-X-X-S 'reading frames' exist on the S4 strand. The tissue selectivity of nifedipine and its analogues may arise, in part, from conservative changes in the amino acid residues at the P and S positions of the reading frame that define the ester-binding regions of receptors from different tissues. The crystal structures of two tissue-selective nifedipine analogues, nimodipine [isopropyl (2-methoxyethyl) 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinecarboxylate ] and nitrendipine [ethyl methyl 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3, 5-pyridinecarboxylate] are reported. Nimodipine was observed to have an unusual ester side chain conformation that enhances the fit to the proposed ester-sensing region of the receptor.

Structure of 6 alpha-methyl-3,20-oxo-1,4,9(11)-pregnatrien-17 alpha-yl acetate.

C24H30O4, Mr = 382.5, orthorhombic, P2(1)2(1)2(1), a = 13.091 (2), b = 19.711 (1), c = 8.242 (1) A, V = 2126.7 (5) A3, Z = 4, Dx = 1.195 Mg m-3, lambda(Cu K alpha) = 1.54184 A, mu(Cu K alpha) = 0.56 mm-1, F(000) = 824, T = 295 K. Final R = 0.045 for 2446 unique reflections. The planar A ring is bent relative to the rest of the steroid skeleton. The B ring has a typical chair conformation and the C and D rings assume 13 beta,14 alpha-half-chair and 13 beta-envelope conformations, respectively. The conformation of the progesterone side chain is similar to the conformation observed in other 17 alpha-ester pregnanes: C16-C17-C20-O20 torsion angle -27.4 (3) degrees.

Structure of 3-hydroxy-1-methyl-1,3,5(10)-estratriene-11,17-dione.

C19H22O3, Mr = 298.39, orthorhombic, P2(1)2(1)2(1), a = 11.332 (6), b = 14.596 (7), c = 9.567 (4) A, V = 1582.6 (5) A3, Z = 4, D chi = 1.252 Mg m-3, lambda(Mo K alpha) = 0.71073 A, mu = 0.0778 mm-1, F(000) = 640, T = 273 K, R = 0.067 for 1762 unique observed reflections where F greater than 2 sigma (F). The structure was studied to observe the effect of 1-methyl and 11-keto substitution. The 3-hydroxyl is hydrogen bonded to O11 at 2.76 A. The B ring is in a 7 alpha, 8 beta half-chair conformation. The molecule twists about the C(9)--C(10) bond to relieve the steric interaction between the 1-methyl and 11-keto groups. The C1--C10--C9--C11 torsion angle is 55 vs 33.5 degrees, the average of 38 estradiol analogue structures.

Structure of 6-methylene-4-pregnene-3,20-dione.

C22H30O2 (1), Mr = 326.47, orthorhombic, P2(1)2(1)2(1), a = 9.662 (3), b = 23.32 (7), c = 8.167 (2) A, V = 1840.3 (4) A3, Z = 4, Dx = 1.178 g cm-3, lambda(Cu K alpha) = 1.5418 A, mu = 5.34 cm-1, F(000) = 712, T = 293 K, R = 0.035, wR = 0.044, S = 1.954 for 2147 unique observed reflections with Fo greater than 2 sigma(Fo). Rings B and C have chair conformations, the A ring assumes an intermediate sofa-half-chair conformation, and the D ring is in the half-chair conformation. The progesterone side chain has the same conformation as observed in 81 steroids; the C16-C17-C20-O20 torsion angle is -18.9 (3) degrees; the C4-C5-C6-C6M torsion angle is -48.6 degrees.

11 beta-hydroxy-9 beta-estrone.

C18H22O3, Mr = 286.37, trigonal, P3(2), a = 10.091 (1), c = 12.271 (1) A, V = 1082.1 A3, Z = 3, Dx = 1.318 Mg m-3, lambda(Cu K alpha) = 1.5418 A, mu = 0.667 mm-1, T = 298 K, F(000) = 462, final R = 0.056 for 1468 observed reflections. The pattern of intermolecular interaction associated with 11 beta-hydroxy substitution differs from that observed in more potent estrogens.

Structure of 1 alpha,3 alpha-trimethylene-2',5-epoxyandrostane-3 beta, 17 beta-diol 17-propionate methanol solvate (1/0.5).

C25H38O4.0.5CH4O, Mr = 418.6, monoclinic, P2(1), a = 19.8504 (20), b = 7.3909 (4), c = 15.7998 (18) A, beta = 93.09 (2) degrees, V = 2314.7 (8) A3, Z = 4, D chi = 1.201 Mg m-3, lambda(Cu K alpha) = 1.54184 A, mu = 0.604 mm-1, F(000) = 916, T = 295 K, R = 0.056 for 4946 unique observed reflections. The crystallographic asymmetric unit contains two steroid molecules and a molecule of methanol. All six-membered rings for both molecules have chair conformations. The D ring has a 13 beta-envelope conformation in molecule 1 and a 13 beta, 14 alpha-half-chair conformation in molecule 2. The most significant differences between the crystallographically independent steroids are in the orientation of the H atoms of the C(3) hydroxyl groups and the conformations of the propionate side chains. When the crystallographically observed molecules are subjected to energy minimization their respective hydroxyl H-atom orientations are retained, but the D rings of both molecules refine to a common 13 beta,14 alpha-half-chair conformation and a significantly different orientation of the C(17) propionate side chain is generated. A comparison with other C(17)-ester-bearing steroids suggests that the energy minimization fails to simulate fully all intramolecular interactions.

Steroid structure and function. Molecular conformation of 4-hydroxyestradiol and its relation to other catechol estrogens.

Hydroxylation of estrogens at C(2) or C(4) effects differentially their binding affinity to and dissociation rate from the estrogen receptor. The X-ray crystal structure of 4-hydroxyestradiol (4-OH-E2) is reported here and compared with that of 2-hydroxyestradiol (2-OH-E2), the 2- and 4-hydroxylated derivatives of estrone (E1) and with that of the parent estrogens, E1 and E2. The overall molecular shape and hydrogen bonding patterns of each were examined for their possible relevance to their binding to the estrogen receptor and their biological activity. A shift in the B-ring conformation away from the symmetrical 7 alpha,8 beta-half-chair form toward the 8 beta-sofa form is induced by both 2- and 4-hydroxy substitution. This shift appears to be larger in the case of E2 than E1 derivatives and to be correlated with an observed change in the hydrogen bonding potential of the C(3) hydroxyl. In 4-OH-E2, as in E2 and 4-OH-E1, the C(3) hydroxyl functions both as a hydrogen bond donor and acceptor. In contrast in 2-OH-E2 the hydroxyl functions only as a donor. The markedly reduced affinity of 2-hydroxylated estrogens for the estrogen receptor could be due to a combination of steric interactions, competition between O(2) and O(3) for hydrogen bonds for a common site on the receptor, and to general interference with hydrogen bond formation of O(3). The C(4) hydroxyl participates in the formation of a chain of hydrogen bonds in the solid state that is similar to a chain seen in single crystals of E2. The presence of a similar chain of hydrogen bonds involving O(3) in the receptor site could account for the decreased dissociation rate of the 4-OH-E2 receptor complex.

Molecular structures of metabolites and analogues of diethylstilbestrol and their relationship to receptor binding and biological activity.

A series of indanyl derivatives of diethylstilbestrol (DES) have recently been identified as inv vivo metabolites of DES. These compounds are of interest because they possess effective uterine estrogen receptor-binding affinity but poor biological activity. The X-ray crystal structures of three of these derivatives were determined and their conformations were compared with those of estradiol and DES. The more active derivatives, indenestrol A (I) and indenestrol B (II) have nearly identical conformations, in which the overall molecule is highly planar, the phenyl ring is twisted out of the plane of the indene rings by approximately 30 degrees, and the distance between the hydroxyl groups is 11.6 A. In the least active derivative, idanestrol (III), the methyl, ethyl, and phenyl substituents were found to be in the same side of the indane ring so that the molecule is constrained to an L-shape. The crystallographically observed conformations of I, II, III, DES, and estradiol, their competative binding affinities, and their in vivo biological activities are consistent with the proposal that the steroid A-ring plays a dominant role in initiating receptor binding while the D-ring orientation relative to the A-ring has a more decisive influence upon activity. The reduction in estrogen receptor-binding affinity and associated reduced activity of III is almost certainly due to its L-shape conformation. The extended conformation of I and II in which both phenolic rings are exposed permitting ready access to both surfaces of either ring probably accounts for the ability of these derivatives to compete so successfully with estradiol for estrogen receptor binding. There are eight different ways in which the molecules of the racemic mixtures of I and II could initiate receptor binding. The reduced biological activity of I and II is probably due to the fact that not all eight binding orientations are compatible with eliciting estrogenic response. Comparison of the observed conformations of I, II, DES, and estradiol suggests that it is the alpha-ring of I and II that minics the steroid A-ring in receptor binding, and that two of the four possible alpha-ring/A-ring matches are most conducive to eliciting hormone activity.

Dipeptide-hydroxamates are good inhibitors of the angiotensin I-converting enzyme.

The inhibition constants (Ki) and modes of inhibition have been determined for a series of dipeptide-hydroxamate compounds with bovine lung parenchyma angiotensin I-converting enzyme (peptidyldipeptide carboxy-hydrolase, E.C. 3.4. 15.1). The hydroxamido function was borne by aspartic, glutamic, or aminoadipic acid and extended by 2, 3 or 4 bond lengths from the proline amide bond. L-glu(NHOH)-L-pro (Ki = 3.4 microM) and D,L-aminoadipicyl (NHOH)-L-pro (Ki = 1.2 microM) were the best competitive inhibitors of the hydrolysis of benzoyl-gly-his-gly but were not effective as affinity ligands for purification of the enzyme.

Synthesis and characterization of the anomeric pair of 17 beta-glucuronides of ethynylestradiol.

The alpha- and beta-anomers of the 17 beta-D-glucuronide conjugate of ethynylestradiol were synthesized by the SnCl4-promoted reaction between beta-acetoxy GAM and the t-17 beta-hydroxyl group of EE2-3-acetate. The conjugates were resolved by crystallization and HPLC. Positive identification was established by u.v. spectrophotometry, i.r. and mass spectrometry and 1H- and 13C-n.m.r. The structure of the beta-anomer was confirmed by X-ray crystallographic analysis. In addition, the alpha-anomer was refractory to hydrolysis by bovine beta-glucuronidase, establishing a biochemical difference between the conjugate pair.

The molecular structure of (20R)-20-phenyl-5-pregnene-3 beta, 20-diol, an inhibitor of cholesterol conversion to pregnenolone.

The crystal and molecular structure of (20R)-20-phenyl-5-pregnene-3 beta, 20-diol hemihydrate has been determined by X-ray analysis in order to establish the configuration and conformation at C(20). Interest in this compound was stimulated by its high affinity inhibitory binding to cytochrome P-450SCC, the enzyme which catalyzes the biosynthesis of pregnenolone (3 beta-hydroxy-5-pregnen-20-one) from cholesterol. The results of the analysis suggest a possible conformation for the cholesterol side chain in the enzyme complex.