New applications for bismuth(III) salts in organic synthesis: from bulk chemicals to steroid and terpene chemistry

Bismuth(III) salts are currently considered efficient and "ecofriendly" reagents and catalysts for the development of new applications in organic synthesis. The preparation of bismuth(III) triflate and its analogues is reviewed as well as some of their applications to the synthesis of bulk chemicals via electrophilic addition and cyclization reactions. The use of bismuth(III) salts in the development of new chemical processes involving steroids and terpenes as substrates is also discussed.

3β-Acet-oxy-lup-20(29)-en-28-yl 1H-1,2,4-tri-azole-1-carboxyl-ate

The title triterpene, C(35)H(53)N(3)O(4), is a C-28 carbamate derivative of 3β-acet-oxy-betulin prepared in a one-step reaction from the commercially available 1,1'-carbonyl-di(1,2,4-triazole) (CDT), crystallized from acetone/n-hexane. All rings are trans fused. The carbamate and acetate substituents are in axial and equatorial positions, respectively. A quantum chemical ab initio Roothaan Hartree-Fock calculation of the equilibrium geometry of the isolated mol-ecule gives values for bond lengths and valency angles in close agreement with experimental values. The calculation also reproduces the observed mol-ecular conformation, with puckering parameters that agree well with those determined from the crystallographic study.

3-Oxo-18α-olean-28,13β-olide

The title terpene, C₃₀H₄₆O₃, is a 28,13β-lactone of oleanolic acid prepared with bis­muth trifluoro­methane­sulfonate (OTf), Bi(OTf)₃·xH₂O. All rings are trans-fused. The X-ray study shows the inversion of the orientation of 18-H in the lactonization reaction. A quantum chemical ab-initio Roothaan Hartree–Fock calculation of the equilibrium geometry of the isolated mol­ecule gives values for bond lengths and valency angles in close agreement with experimental values. The calculation also reproduces the observed mol­ecular conformation, with puckering parameters that agree well with those determined from the crystallographic study.

3β-Hy-droxy-lup-20(29)-en-28-yl 1H-imidazole-1-carboxyl-ate

The title triterpene, C(34)H(52)N(2)O(3), is a C-28 carbamate derivative of betulin prepared in a one-step reaction from the commercially available 1,1'-carbonyl-diimidazole (CDI). All rings are fused trans. The X-ray study shows the retention of the configuration of C-28 with respect to the known chiral centres of the molecule. In the crystal, the mol-ecules are O-H⋯O hydrogen bonded via the hy-droxy group and the carbonyl group of the carbamate function into chains running along the c axis. A quantum-mechanical ab initio Roothaan Hartree-Fock calculation of the equilibrium geometry of the isolated mol-ecule gives values for bond-lengths and valency angles close to the experimental values. The calculations also reproduce the mol-ecular conformation well, with calculated puckering parameters that agree well with the observed values.

19β,28-Ep-oxy-18α-olean-3β-ol

The title triterpene, C₃₀H₅₀O₂, is an 18α-oleanane derivative prepared by the Wagner–Meerwein rearrangement of betulin with Bi(OTf)₃.xH₂O (OTF is trifluoromethanesulfonate). There are two symmetry-independent mol­ecules in the asymmetric unit that show no significant differences concerning bond lengths and angles. The conformation of the six-membered rings is close to a chair form, while the five-membered epoxide rings adopt envelope conformations. All rings are trans-fused. In the crystal, mol­ecules are held together by O—H⋯O hydrogen bonds. A quantum-mechanical ab initio Roothan Hartree–Fock calculation on the isolated mol­ecule gives values for bond lengths and valency angles close to the experimental values. The calculations also reproduce well the mol­ecular conformation with calculated puckering parameters that match well the observed values.

16α,17α-Ep-oxy-5α-hydr-oxy-6β-nitrooxy-20-oxopregnan-3β-yl acetate

The title steroid, C(23)H(33)NO(8), is a pregnane derivative obtained regio-, stereo- and chemoselectively from the ring opening of the corresponding 5α,6α;16α,17α-diepoxide with bis-muth(III) nitrate. There are two symmetry-independent mol-ecules in the asymmetric unit that show no significant differences concerning bond lengths and angles. All rings are trans-fused. The conformations of the six-membered rings are close to chair forms, while the five-membered ring adopts an envelope conformation. The mol-ecules are held together by an extensive O-H⋯O hydrogen-bonding network of chains runnning along the a axis.

6beta-Hydroxy-5beta-methyl-20-oxo-19-norpregn-9(10)-en-3beta-yl acetate

In the title compound, C(23)H(34)O(4), which is an intermediate in the synthesis of pregnane derivatives with a modified skeleton that show potent abortion-inducing activity, the conformation of ring B is close to half-chair due to the presence of both the C=C double bond and the axial 5beta-methyl group. Rings A and C have conformations close to chair, while ring D has a twisted conformation around the bridgehead C-C bond. Molecules are hydrogen bonded via the hydroxyl and acetoxy groups into infinite chains. Quantum-mechanical ab initio Roothan Hartree-Fock calculations show that crystal packing might be responsible for the low values of the angles between rings A and B, and between ring A and rings C and D, as well as for a different steric position of the methyl ketone side chain compared to the geometry of the free molecule.

6β-Acetamido-5α-hydroxy-cholestan-3β-yl acetate

The title steroid, C₃₁H₅₃NO₄, was prepared from the corresponding 5α,6α-epoxy­cholestane. The conformation of the six-membered rings is close to a chair form, while the five-membered ring adopts a twist conformation. The hydroxyl and acetamide groups are in axial positions. The nucleophilic species bound to the steroid nucleus at position 6 by the β-face, whereas the hydroxyl group at position 5 has α-orientation. All rings are trans-fused. The crystal packing shows that the mol­ecules related by twofold symmetry exist as O—H⋯O hydrogen-bonded dimers.

CYP17 inhibitors for prostate cancer treatment--an update

It is almost 70 years since the discovery by Huggins et al. that androgens are essential for prostate cancer (PC) growth and progression, and there has been about 30 years experience using ketoconazole for PC therapy. Since then we have come a long way in learning about the disease and developing new strategies to approach it, among which is cytochrome 17alpha-hydroxylase-C(17,20)-lyase (CYP17) inhibition. This review focuses on the efforts to find prospective CYP17 inhibitors, both steroidal and nonsteroidal, in the absence of a 3D structure of the enzyme. It covers almost 4 decades of literature with highlights on the most significant achievements in this area, providing insight into PC pathophysiology, management and treatment options.

6beta-Azido-7alpha-hydroxy-17-oxo-5alpha-androstan-3beta-yl acetate

In the title compound, C21H31N3O4, a potential inhibitor of aromatase, all rings are fused trans. Rings A, B and C have chair conformations which are slightly flattened. Ring D has a 14alpha-envelope conformation. The steroid nucleus has a small twist, as shown by the C19-C10...C13-C18 torsion angle of 6.6 (2) degrees. Ab initio calculations of the equilibrium geometry of the molecule reproduce this small twist, which appears to be due to the steric effect of the 6beta-azide substituent rather than to packing effects.

17-Oxo-5α-androst-6-en-3β-yl acetate

In the title compound, C(21)H(30)O(3), a potential inhibitor of aromatase, all rings are fused trans. Rings A and C have chair conformations which are slightly flattened, whereas the conformation of ring B is close to a half-chair. Ring D has a 14 alpha-envelope conformation. The steroid nucleus has a small twist, as shown by the C19-C10...C13-C18 (steroid numbering) torsion angle of -6.9 (3) degrees. Ab initio calculations of the equilibrium geometry of the molecule reproduce this small twist, which appears to be due to the conformation of ring B rather than to packing effects.