Allopregnanolone and Pregnanolone Analogues Modified in the C Ring: Synthesis and Activity

Abstract

Abstract(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-5-pregnan-20-one), the principal neurosteroid acting via γ-aminobutyric acid (GABA). These analogues were designed to study the structural requirements of the corresponding GABA A receptor. Their biological activity was measured by in vitro test with groups at the C-ring edge, rather than on specific interactions between them and the receptor.3 IntroductionAlthough steroids in general are widely understood as a class of natural products, which hold only little potential of a new breakthrough, neurosteroids are still studied with great interest (see the "Neurosteroid" copy 1,2 of Pharmacol. Ther. 2007 or recent papers [3][4][5][6] ). Unlike the family of other steroid hormones, neurosteroids do not bind to nuclear but to membrane receptors for neurotransmitters. One of the neurotransmitters -γ-aminobutyric acid (GABA) elicits the influx of chloride ions into neuronal cells, which changes the membrane potential of a given cell, which in turn prevents the transmission of subsequent neuronal signals.In agreement with this action, neurosteroids such as allopregnanolone or pregnanolone (1a and 1b, respectively, see Figure 1), 3α,5α-tetrahydrodeoxycorticosterone (2), and some of their analogues, acting via the GABA A receptor, have anxiolytic, anaesthetic, anticonvulsant, and sedative properties. 7,8 Many new types of such analogues were prepared in order to refine the knowledge of relationship between the structure of compounds and their neuronal activity.These analogues either involve compounds with additional substituents (eg., alphaxalone, 3), or have their skeleton modified by increasing 9 or decreasing 10-12 the flexibility of the molecule or even reversing its chirality. 13 Various changes were also made to the steroid side chain. [14][15][16][17] Even heteroatoms (O, N, S) were introduced into the steroid framework with varied success. 18-21Almost all the active analogues contained a hydroxyl group in position 3α. Its presence has been considered essential for the activity, even though a 3α-amino analogue, lacking the 3α-hydroxyl (i. e., 4) retained 56% of the activity of allopregnanolone. 22In our search for new analogues of allopreganolone, we prepared a number of 5-pregnane derivatives designed to exert a higher solubility in water than the principal neurosteroid 1a.The biological activity of the new products was assessed using in vitro tests, which measured 4 the binding of labelled ligands to GABA A receptors in the absence and presence of the tested compounds. In our previous paper we reported structure modification of the steroidal B ring. 11Some anomalies in the structure of the analogues were tolerated by the GABA A receptor, others not; the biological consequences of the structure modification were rationalized using...

Synthesis and pharmacological evaluation of neurosteroid photoaffinity ligands

“…1 & 2 , shown above) bind with the upper edge of their steroid framework pointing out of the cavity, whereas the unnatural enantiomers (not shown) bind with the upper edge of their steroid framework pointing into the cavity. 12 Consistently, the 11-position of the natural enantiomer of the steroid can be functionalized with sterically large groups, 12,13 but in contrast, the 6-position of the natural enantiomer can be modified with only a small group, such as a diazirine. 15,16 The presence of the oxygenated group at the 11-position is nonessential, but if hydroxylated, the 11β-configuration is preferred.…”