Neurosteroids: 7-aza-allopregnanolone—a poor substitute for allopregnanolone

Neurosteroids: Can a 2alpha,3alpha-epoxy ring make up for the 3alpha-hydroxyl group?

Seven steroid epoxides were prepared from 5α-pregn-2-en-20-one and 5α-pregn-3-en-20-one and their side-chain derivatives. All compounds were tested in vitro for binding to γ-aminobutyric acid (GABAA) receptor, some of them also in vivo for anticonvulsant action. 2α,3α-Epoxy-5α-pregnan-20-one inhibited the TBPS binding to the GABAA receptor and showed a moderate anticonvulsant action in immature rats. In contrast, its 3α,4α-isomer was inactive. More polar epoxide derivatives, modified at the side chain were less active or inactive. Noteworthy, diol 20, the product of trans-diaxial opening of the 2α,3α-epoxide 4, was not able to inhibit the TBPS binding, showing that the activity of the epoxide is due to the compound itself and not to its hydrolytic product. The 3α-hydroxyl group is known to be essential for the GABAA receptor binding. Despite the shortness of in vivo effects which are probably due to metabolic inactivation of the products prepared, our results show that the 2α,3α-epoxy ring is another structural pattern with ability to bind the GABAAR.

Synthetic applications of hypophosphite derivatives in reduction

The purpose of this review is to collect the applications in fine synthesis of hypophosphite derivatives as reducing agents.

Allopregnanolone and pregnanolone analogues modified in the C ring: synthesis and activity

(25R)-3β-Hydroxy-5α-spirostan-12-one (hecogenin) and 11α-hydroxypregn-4-ene-3,20-dione (11α-hydroxyprogesterone) were used as starting materials for the synthesis of a series of 11- and 12-substituted derivatives of 5ξ-pregnanolone (3α-hydroxy-5α-pregnan-20-one and 3α-hydroxy-5β-pregnan-20-one), the principal neurosteroid acting via γ-aminobutyric acid (GABA). These analogues were designed to study the structural requirements of the corresponding GABAA receptor. Their biological activity was measured by in vitro test with [(3)H]flunitrazepam as radioligand in which allopregnanolone and its active analogues stimulated the binding to the GABAA receptor. Analysis of the SAR data suggests dependence of the flunitrazepam binding activity on the hydrophobic-hydrophilic balance of the groups at the C-ring edge rather than on specific interactions between them and the receptor.

The Chemistry of B-Norsteroidal 6-Ketones and their Relatives

The preparation and reactions of B-norsteroidal 6-ketones and their relatives are reviewed in the context of the stability of the A/B and B/C ring junctions and the stereochemistry of the addition reactions to the carbonyl group. This review is a sequel to a previous article on the reactions of B-norsteroidal 4- and 5-enes.

Synthesis of a core carbon framework of cyanosporasides A and B

Treatment of 3-(2-ethynylphenyl)prop-2-ynyl benzenesulfinate with 2.5 mol % of [RhCl(CO)(2)](2) at 40 degrees C under an atmosphere of CO effected the successive 2,3-sigmatropic rearrangement and carbonylative [2 + 2 + 1] ring-closing reaction to afford the 8-(phenylsulfonyl)-1H-cyclopent[a]-inden-2-one in a high yield. Chemical modification of the ring-closed product via lipase-mediated optical resolution produced the optically active 3-acetoxy-3a-cyclohexyloxy-3,3a-dihydrocyclopent-[a]indene skeleton, the core carbon framework of cyanosporasides A and B.

The reactions of B-norsteroidal 4- and 5-enes

Aspects of the stereochemistry of addition reactions to B-norsteroidal 4- and 5-alkenes are compared to the corresponding reactions in normal 6:6 A/B series.