19-Nor-10-azasteroids, a New Class of Steroid 5α-Reductase Inhibitors. 2. X-ray Structure, Molecular Modeling, Conformational Analysis of 19-Nor-10-azasteroids and Comparison with 4-Azasteroids and 6-Azasteroids

Abstract

19-Nor-10-azasteroids are a new class of 5α-reductase inhibitors whose activity depends on the presence of the bridgehead N-10 atom conjugated with the 4-en-3-one moiety in the A ring. The X-ray structure of 19-nor-10-azasteroid 1 has been determined and it is compared with the X-ray structure of testosterone. A complete conformational analysis of these compounds has been performed, determining the number and energy of the possible conformers, as well as the molecular flexibility of the 10-azasteroidal skeleton. Thus, MM2* molecular mechanics calculations and AM1 semiempirical energy refinements revealed that 19-nor-10-azasteroids 1−3 have four possible conformations with very small energy differences and that they are very flexible molecules. The conformational analysis has been extended to testosterone (4), which also showed conformational flexibility, with three different conformations, and to 6-azasteroid 5 and 4-azasteroid 6, for which only two thermally accessible conformations have been found. Compared to 19-nor-10-azasteroids 1−3, azasteroids 5 and 6 appear to be more rigid structures. By a best fit analysis of all conformers of 1−5 with the global minimum of testosterone (4-I) it has been found that the lowest energy conformers of 1, 3, and 5 are very close to the structure of 4-I, and among the conformers of 2, the best similarity has been observed for the highest energy conformer 2-IV.

A Concise Route to 19-Nor-10-azasteroids, a New Class of Steroid 5α-Reductase Inhibitors. 3.1 Synthesis of (+)-19-Nor-10-azatestosterone and (+)-17β-(Acetyloxy)-(5β)-10-azaestr-1-en-3-one

“…Recently, we have reported on the synthesis and biological evaluation of a novel class of potent azasteroidal inhibitors (19-nor-10-azasteroids) having as a new feature a bridgehead nitrogen atom at position 10 of the steroidal skeleton . We based the synthesis of these compounds on the sequential rearrangement-cyclization of isoxazoline-5-spirocyclopropanes, a methodology well established in our laboratory, which allows the incorporation of a 4-pyridone moiety in a polycyclic system. 1a, However, the preparation of the suitably functionalized isoxazolines required several synthetic steps, and moreover, the final thermal rearrangements always gave the azasteroids in low yield and in mixture with other products.…”

“…Recently, we have reported on the synthesis and biological evaluation of a novel class of potent azasteroidal inhibitors (19-nor-10-azasteroids) having as a new feature a bridgehead nitrogen atom at position 10 of the steroidal skeleton . We based the synthesis of these compounds on the sequential rearrangement-cyclization of isoxazoline-5-spirocyclopropanes, a methodology well established in our laboratory, which allows the incorporation of a 4-pyridone moiety in a polycyclic system. 1a, However, the preparation of the suitably functionalized isoxazolines required several synthetic steps, and moreover, the final thermal rearrangements always gave the azasteroids in low yield and in mixture with other products. Therefore, owing to the need of a more efficient procedure for the preparation of 10-azasteroids, we planned a new strategy based on the tandem N -(acyloxy)iminium ion−Michael addition reaction, recently described by Pilli and co-workers for the synthesis of bicyclic N -bridgehead alkaloids, which should provide the 19-nor-10-azasteroidal skeleton in only six steps from commercially available (+)-3-[(3a S )-(3aα,4α,7aβ)-1,5-dioxo-7a-methyloctahydro-(1 H )-inden-4-yl]propionic acid ( 1 )…”

“…For the synthesis of unsaturated compound 8 (Scheme 2), trimethylsilyl triflate (TMSOTf) was added to a mixture of 1-methoxy-3-[(trimethylsilyl)oxy]-1,3-butadiene (Danishefsky's diene), Et 3 N, and 7 at 0 °C in CH 2 Cl 2 , leading, after a 36 h NaHCO 3 treatment, to azasteroid 8 (39%) as a single diastereoisomer. Since the enaminone moiety in the A ring of 19-nor-10-azasteroids is a planar system, with the N atom having a strong sp 2 character,1b the attribution of the α or β orientation to the proton on C-5 is the only stereochemical problem concerning compound 8 . The comparison of the 1 H and 13 C NMR spectra of 8 with those of the corresponding 17-oxo-substituted Δ 1(2) -19-nor-10-azasteroid 1a having 5α-H stereochemistry led to the observation that while 5-H in the latter compound resonates below 3.0 ppm and C-5 at 65.8 ppm, in compound 8 the same proton is found at 3.75 ppm and C-5 resonates at 53.1 ppm.…”

Selective non-steroidal inhibitors of 5α-reductase type 1

“…The first inhibitors have been therefore designed by modifying the structure of natural substrates, including the substitution of one carbon atom of the A or B ring of the steroids by an heteroatom, leading to the discovery of potent inhibitors of human 5␣-reductase such as 4-azasteroids (among which finasteride, marketed for the treatment of BPH) [30][31][32], 6-azasteroids [33,34], 10-azasteroids [35][36][37][38][39], and steroidal carboxylic acid inhibitors [40][41][42][43] (Scheme 2). The kinetic mechanism by which T is reduced to DHT is believed to proceed via a preferentially ordered binding of the substrate and release of DHT from the enzyme.…”

19-Nor-10-azasteroids. 5.1 A Synthetic Strategy for the Preparation of (+)-17-(3-Pyridyl)-(5β)-10-azaestra-1,16- dien-3-one, a Novel Potential Inhibitor for Human Cytochrome P45017α (17α-Hydroxylase/C17,20-lyase)

“…We have recently reported the synthesis of some 19-nor-10-azasteroids, a new class of 5α-reductase enzyme inhibitors . Since 5α-reductase converts testosterone to the more potent androgen dihydrotestosterone in prostatic tissues, cooperative inhibition of 5α-reductase and P450 17 α might be beneficial in the treatment of prostate cancer. , Therefore, we reasoned that anchoring a 3-pyridyl moiety on the D ring of 19-nor-10-azasteroids would produce novel steroid derivatives, potentially inhibitors of both 5α-reductase and P450 17 α .…”