Steroids. LXXIX. Synthesis and reactions of oxiranes obtained from 3- and 17-keto steroids

3-Benzylaminomethyl Lithocholic Acid Derivatives Exhibited Potent and Selective Uncompetitive Inhibitory Activity Against Protein Tyrosine Phosphatase 1B (PTP1B)

Protein tyrosine phosphatase 1B (PTP1B) is a promising drug target for treating type 2 diabetes (T2DM) and obesity. As a result, developing new therapies that target PTP1B is an attractive strategy for treating these diseases. Herein, we detail the synthesis of 15 lithocholic acid (LA) derivatives, each containing different benzylaminomethyl groups attached to the C3 position of the steroid skeleton. The derivatives were assessed against two forms of PTP1B enzyme (hPTP1B1-400 and hPTP1B1-285), and the most potent compounds were then tested against T-cell protein tyrosine phosphatase (TCPTP) to determine their selectivity. The results showed that compounds 6m and 6n were more potent than the reference compounds (ursolic acid, chlorogenic acid, suramin, and TCS401). Additionally, both compounds exhibited greater potency over hPTP1B1-400. Furthermore, enzyme kinetic studies on hPTP1B1-400 revealed that these two lithocholic acid derivatives have an uncompetitive inhibition against hPTP1B1-400 with K i values of 2.5 and 3.4 μM, respectively. Interestingly, these compounds were around 75-fold more selective for PTP1B over TCPTP. Finally, docking studies and molecular dynamics simulations (MDS) were conducted to determine how these compounds interact with PTP1B. The docking studies revealed hydrophobic and H-bond interactions with amino acid residues in the unstructured region. MDS showed that these interactions persisted throughout the 200 ns simulation, indicating the crucial role of the unstructured zone in the biological activity and inhibition of PTP1B.

Stereoselective synthesis of F-ring saturated estrone-derived inhibitors of Hedgehog signaling based on cyclopamine

Previous work in this laboratory established that the readily available F-ring aromatic analog of cyclopamine is a highly potent inhibitor of Hedgehog signaling. The synthesis and biological evaluation of two F-ring saturated analogs that are more potent than the F-ring aromatic structure are reported.

17beta-Nitro-5alpha-androstan-3alpha-ol and its 3beta-methyl derivative: neurosteroid analogs with potent anticonvulsant and anxiolytic activities

Many 17-substituted androstan-3alpha-ol analogs act as positive allosteric modulators of GABA(A) receptors and exert anticonvulsant and anxiolytic-like activity actions in animal models. The endogenous neurosteroid allopregnanolone (17beta-acetyl; 1) is among the most potent of these. Here we demonstrate that 3alpha-hydroxy-17beta-nitro-5alpha-androstane (2b) and its 3beta-methyl analog (3alpha-hydroxy-3beta-methyl-17beta-nitro-5alpha-androstane; 2c) modulate GABA(A) receptors as assessed by [(35)S]t-butylbicyclo-phosphorothionate and [(3)H]flunitrazepam binding with potencies equivalent to or greater than 1. These compounds also had potencies equivalent to or greater than 1 in the pentylenetetrazol and 6Hz seizure models in the mouse. Furthermore, 2b exhibited anxiolytic-like activity in the elevated zero maze. The 3beta-hydroxy, 3alpha-desmethyl analog (2a) was devoid of activity on GABA(A) receptors in vitro but had moderate activity in the seizure models, possibly as a result of epimerization in vivo at the 3-position. This conclusion was supported by the lack of in vivo activity of the 3beta-hydroxy, 3alpha-methyl analog (2d), which is not expected to undergo epimerization. We conclude that nitro can serve as a bioisostere for acetyl at the 17beta-position of 5alpha-androstan-3alpha-ol, such that the nitro analog fully retains the bioactivity of the endogenous neurosteroid at GABA(A) receptors.

Syntheses and ligand-binding studies of 1 alpha- and 17 alpha-aminoalkyl dihydrotestosterone derivatives to human sex hormone-binding globulin

We report on the syntheses of 1 alpha- and 17 alpha-aminoalkyl dihydrotestosterone (DHT) derivatives and the particularly high binding affinity of the 1 alpha-aminohexyl ligand for human sex hormone-binding globulin (SHBG). The two 17 alpha-aminopropyl-17 beta-hydroxy-5 alpha-androstan-3-one (1) and 17 alpha-aminocaproylamidoethyl-17 beta-hydroxy-5 alpha-androstan-3-one (2) derivatives were synthesized via a 17beta-spirooxirane intermediate in high yields. The 1 alpha-aminohexyl-17 beta-hydroxy-5 alpha-androstan-3-one compound (3) was obtained in a seven step synthesis using a copper-catalyzed conjugate addition of a omega-silyloxyhexyl Grignard reagent to 17 beta-benzoyloxy-5 alpha-androst-1-en-3-one. All structures were elucidated based on 1H NMR spectroscopy and mass spectral analyses. The three aminosteroid derivatives were tested as ligands for SHBG by competition experiments with tritiated testosterone as tracer under equilibrium conditions. The association constants of the two 17 alpha-DHT derivatives were approximately 1 x 10(7) M(-1), whereas the 1 alpha-DHT derivative showed a remarkably high binding affinity to SHBG with an association constant of 1.40 x 10(9) M(-1). These aminoalkyl derivatives, substituted either at the D-ring or the A-ring of the steroid skeleton, can be easily coupled onto a carboxymethylated solid state surface of a biosensor. Such a device lends itself to kinetic and thermodynamic studies aimed to provide a better understanding of the biospecific interaction of steroids with SHBG.

Parallel solid-phase synthesis of 3beta-peptido-3alpha-hydroxy-5alpha-androstan-17-one derivatives for inhibition of type 3 17beta-hydroxysteroid dehydrogenase

Type 3 17beta-hydroxysteroid dehydrogenase (17beta-HSD), a key steroidogenic enzyme, transforms 4-androstene-3,17-dione (Delta(4)-dione) into testosterone. In order to produce potential inhibitors, we performed solid-phase synthesis of model libraries of 3beta-peptido-3alpha-hydroxy-5alpha-androstan-17-ones with 1, 2, or 3 levels of molecular diversity, obtaining good overall yields (23-58%) and a high average purity (86%, without any purification steps) using the Leznoff's acetal linker. The libraries were rapidly synthesized in a parallel format and the generated compounds were tested as inhibitors of type 3 17beta-HSD. Potent inhibitors were identified from these model libraries, especially six members of the level 3 library having at least one phenyl group. One of them, the 3beta-(N-heptanoyl-L-phenylalanine-L-leucine-aminomethyl)-3alpha-hydroxy-5alpha-androstan-17-one (42) inhibited the enzyme with an IC(50) value of 227nM, which is twice as potent as the natural substrate Delta(4)-dione when used itself as an inhibitor. Using the proliferation of androgen-sensitive (AR(+)) Shionogi cells as model of androgenicity, the compound 42 induced only a slight proliferation at 1 microM (less than previously reported type 3 17beta-HSD inhibitors) and, interestingly, no proliferation at 0.1 microM.

17 alpha-substituted analogs of estradiol for the development of fluorescent estrogen receptor ligands

For the successful development of a high-affinity fluorophore-estradiol conjugate, the fluorophore must be attached to the estradiol molecule at a position that interferes least with its binding to the receptor. We have concentrated on 17 alpha substituents as models for fluorophore attachment, based on literature precedent and on our earlier work with small 17 alpha side chains. In this report, we describe syntheses and estrogen receptor binding affinities of 19 analogs of estradiol substituted in the 17 alpha position with larger side chains (of six to 11 carbons), some of which may be synthetically modified to link a fluorophore. These analogs were synthesized either by nucleophilic cleavage of estrone-17 beta-oxirane 3-benzyl ether and subsequent debenzylation (4 to 18), by cross-coupling of alkynes (21 to 24), by alkylation of 17 alpha-ethynylestradiol 3,17-bis(tetrahydropyranyl ether) and subsequent acidic hydrolysis (25 to 28), or by reacting estrone either with appropriate aryl/alkynyllithium reagents (29, 30, and 32) or with benzylmagnesium bromide (31). Relative binding affinities of these newly synthesized analogs were determined for estrogen receptor (rat uterus) using a standard competition assay. The results suggest that analogs with reduced mobility and/or more polarizable electron density in the side chain generally bind more strongly to the receptor. The relative affinities of several selected compounds were also determined in the presence of 4% dimethylformamide; some compounds bearing larger, nonpolar 17 alpha substituents showed dramatically improved affinities, while affinities for compounds with shorter nonpolar side chains remained largely unchanged. These binding affinity results should be useful in designing new high-affinity fluorescent ligands for the estrogen receptor.

Detection of a transient enzyme-steroid complex during active-site-directed irreversible inhibition of 3-oxo-delta 5-steroid isomerase

The reaction of the active-site-directed irreversible inhibitor (17S)-spiro[estra-1,3,5(10),6,8-pentaene-17,2'-oxiran]-3-ol (5 beta) with 3-oxo-delta 5-steroid isomerase has been monitored by repetitive scanning ultraviolet spectroscopy of a solution of 5 beta plus isomerase against a blank containing only 5 beta. Upon initial mixing of 5 beta with the isomerase an absorbance maximum at ca. 250 nm appears. With time, this peak decreases and is replaced with a new peak near 280 nm. These results directly demonstrate the existence of a transient enzyme-steroid intermediate in the inactivation reaction. The ultraviolet spectrum suggests that the steroid in the transient complex resembles the ionized phenol, while the phenolic group in the irreversibly bound complex is un-ionized. These spectral studies support our previous proposal that there are two enzyme-steroid complexes that are related by a 180 degree rotation about an axis perpendicular to the plane of the steroid nucleus. This hypothesis offers an explanation for the reaction of 17 beta-oxiranes with the same residue (Asp-38) that is thought to be involved in the catalytic mechanism. Two new oxiranes, (17S)-spiro[estra-1,3,5(10)-triene-17,2'-oxiran]-3 beta-ol (6 beta) and (17S)-spiro[5 alpha-androstane-17,2'-oxiran]-3-one (8 beta), were also found to be potent active-site-directed irreversible inhibitors of the isomerase (k3/KI = 31 M-1 s-1 and 340 M-1 s-1, respectively). The relationship of these results to the nature of the active site of the isomerase is discussed.

17 alpha-allyl estradiol analogues as candidates for development of high-affinity fluorescein-estradiol conjugates

In order to develop stable, high-affinity fluorescein-estradiol conjugates, the fluorescein moiety must be leashed to the estradiol molecule at a point which interferes least with estradiol's binding to the receptor. Because of the high affinity of 17 alpha-substituted estradiol (e.g. ethynyl estradiol), we investigated a series of 17 alpha-substituted estradiol compounds to determine the optimal properties of a leash at this position. Twelve estradiol derivatives bearing a three-carbon 17 alpha side chain with or without a terminal functional group and with varying degrees of unsaturation were synthesized. Initial comparison of the receptor binding affinities of some of these derivatives suggested that three factors might reduce affinity: internal hydrogen bonding of the 17 beta-hydroxyl proton with an oxygen atom of the 17 alpha side chain; hydrophilicity of the ligand; or steric interference of the side chain with receptor binding. Further comparisons were designed to evaluate the relative contribution of these factors. The results suggest that the relative affinities of these 17 alpha-substituted estradiol derivatives are influenced primarily by the steric interference of the side chains and also by their hydrophilicity. Internal hydrogen bonding involving the 17 beta-hydroxyl proton does not seem to have a profound effect.