Construction of key building blocks towards the synthesis of cortistatins.

This work reports the construction of key building blocks towards the synthesis of cortistatins; a family of steroidal alkaloids. Cortistatin A, being a primary target due to its superior biological properties over other congeners, has been prepared by two different synthetic routes. Synthesis of the precursor to the heavily substituted A-ring starting from d-glucose and construction of the DE-ring junction employing a Hajos-Parrish ketone as a chiral pool have been demonstrated. Efforts are underway to assemble these key fragments and build towards the total synthesis of cortistatin A.

Antihormonal potential of selected D-homo and D-seco estratriene derivatives.

Since many estrogen derivatives exhibit anti-hormone or enzyme inhibition potential, a large number of steroidal derivatives have been synthesised from appropriate precursors, in order to obtain potential therapeutics for the treatment of hormone-dependent cancers. In molecular docking studies, based on X-ray crystallographic analysis, selected D-homo and D-seco estratriene derivatives were predicted to bind strongly to estrogen receptor α (ERα), aromatase and 17,20 lyase, suggesting they could be good starting compounds for antihormonal studies. Test results in vivo suggest that these compounds do not possess estrogenic activity, while some of them showed weak anti-estrogenic properties. In vitro anti-aromatase and anti-lyase assays showed partial inhibition of these two enzymes, while some compounds activated aromatase. Aromatase activators are capable of promoting estrogen synthesis for treatment of pathological conditions caused by estrogen depletion, e.g. osteopenia or osteoporosis.

Synthesis of novel 1,2,3-triazolyl derivatives of pregnane, androstane and D-homoandrostane. Tandem "click" reaction/Cu-catalyzed D-homo rearrangement.

Copper-catalyzed 1,3-dipolar cycloaddition has been employed in the reaction of steroidal azides with various terminal alkynes. A number of novel 1,2,3-triazolyl derivatives of pregnane, androstane and D-homoandrostane were obtained in high yield (70-98%). The developed synthetic protocols allowed us to attach the triazolyl moiety to both the side chain and the steroidal backbone directly, despite the steric hindrance exerted by the polycyclic system. The presence of Cu(II) was shown to evoke d-homo rearrangement under mild conditions. A rational choice of the copper precatalyst permitted us to carry out the "click" reaction either along with tandem d-homo rearrangement or in the absence of this process. The tendency of 16-heterosubstituted steroids to undergo D-homo rearrangement under Cu(II) catalysis was studied.

Synthesis and cytotoxic activity of some 4,6-diaza-A,B-dihomo-steroid bilactams.

Using cholesterol, stigmasterol and sitosterol as starting materials, some 4,6-diaza-A,B-dihomo-steroid bilactams were synthesized via two different synthetic routes by oxidation, reduction, oximation, Beckman rearrangement, etc. The cytotoxic activity of the synthesized compounds against SGC 7901 (human ventriculi carcinoma), Bel-7404 (human liver carcinoma), HeLa (human cervical carcinoma) and HT-29 (colonic carcinoma) cancer cells were investigated. The results showed that compounds 2 and 7b displayed a good cytotoxic activity to the SGC 7901, Bel 7404 and HeLa tumor cell lines with the IC50 values of 11.6, 16.4, 13.9 and 13.1, 21.8, 13.1 µmol/L, respectively. Their cytotoxic activity is almost same as cisplatin to these cells. The information obtained from the studies may be useful for the design of novel chemotherapeutic drugs.

A new strategy for selective targeting of progesterone receptor with passive antagonists.

Currently available progesterone (P4) receptor (PR) antagonists, such as mifepristone (RU486), lack specificity and display partial agonist properties, leading to potential drawbacks in their clinical use. Recent x-ray crystallographic studies have identified key contacts involved in the binding of agonists and antagonists with PR opening the way for a new rational strategy for inactivating PR. We report here the synthesis and characterization of a novel class of PR antagonists (APRn) designed from such studies. The lead molecule, the homosteroid APR19, displays in vivo endometrial anti-P4 activity. APR19 inhibits P4-induced PR recruitment and transactivation from synthetic and endogenous gene promoters. Importantly, it exhibits high PR selectivity with respect to other steroid hormone receptors and is devoid of any partial agonist activity on PR target gene transcription. Two-hybrid and immunostaining experiments reveal that APR19-bound PR is unable to interact with either steroid receptor coactivators 1 and 2 (SRC1 and SCR2) or nuclear receptor corepressor (NcoR) and silencing mediator of retinoid acid and thyroid hormone receptor (SMRT), in contrast to RU486-PR complexes. APR19 also inhibits agonist-induced phosphorylation of serine 294 regulating PR transcriptional activity and turnover kinetics. In silico docking studies based on the crystal structure of the PR ligand-binding domain show that, in contrast to P4, APR19 does not establish stabilizing hydrogen bonds with the ligand-binding cavity, resulting in an unstable ligand-receptor complex. Altogether, these properties highly distinguish APR19 from RU486 and likely its derivatives, suggesting that it belongs to a new class of pure antiprogestins that inactivate PR by a passive mechanism. These specific PR antagonists open new perspectives for long-term hormonal therapy.

A biomimetic approach to C-nor-D-homo-steroids.

A biomimetic three-step transformation of classical "6-6-6-5"-steroids into their C-nor-D-homo-counterparts gives an easy and fast access to this highly important substructure of natural products, as it is found in cyclopamine, and nakiterpiosin. A novel reagent combination allows for the rearrangement even of 17-keto steroids with high endoselectivity. In several examples the broadness of this strategy is outlined.

Novel 13ß- and 13α-D-homo steroids: 17a-carboxamido-D-homoestra-1,3,5(10),17-tetraene derivatives via palladium-catalyzed aminocarbonylations.

17a-Methoxycarbonyl- and 17a-carboxamido-D-homoestra-1,3,5(10),17-tetraene derivatives were synthesized by palladium-catalyzed carbonylation reactions of the corresponding 17a-iodo-D-homoestra-1,3,5(10),17-tetraene derivatives using methanol and various amines as O- and N-nucleophiles, respectively. Both the natural (13ß) and the epi (13α) series of compounds were isolated. The 17a-iodo-17-ene functionalities in the two 13-epimer series differ in reactivity. While the aminocarbonylations were practically complete in the 13ß series in reasonable reaction time under mild conditions and high isolated yields were achieved, the corresponding 13α-17a-iodo-17-ene substrate has shown decreased reactivity resulting in moderate to low yields. However, under high carbon monoxide pressure (40 bar) excellent yields can be obtained even in the 13α series. The aminocarbonylation was completely chemoselective in both series, i.e., the corresponding 17a-carboxamido-17-ene derivatives were formed exclusively.

Chemical and biological studies of nakiterpiosin and nakiterpiosinone.

Nakiterpiosin and nakiterpiosinone are two related C-nor-D-homosteroids isolated from the sponge Terpios hoshinota that show promise as anticancer agents. We have previously described the asymmetric synthesis and revision of the relative configuration of nakiterpiosin. We now provide detailed information on the stereochemical analysis that supports our structure revision and the synthesis of the originally proposed and revised nakiterpiosin. In addition, we herein describe a refined approach for the synthesis of nakiterpiosin, the first synthesis of nakiterpiosinone, and preliminary mechanistic studies of nakiterpiosin's action in mammalian cells. Cells treated with nakiterpiosin exhibit compromised formation of the primary cilium, an organelle that functions as an assembly point for components of the Hedgehog signal transduction pathway. We provide evidence that the biological effects exhibited by nakiterpiosin are mechanistically distinct from those of well-established antimitotic agents such as taxol. Nakiterpiosin may be useful as an anticancer agent in those tumors resistant to existing antimitotic agents and those dependent on Hedgehog pathway responses for growth.

Synthesis and structure revision of nakiterpiosin.

This manuscript describes a convergent synthesis and the revision of the relative stereochemistry of nakiterpiosin, a marine C-nor-D-homosteroid. Our synthesis features a late-stage carbonylative Stille cross-coupling reaction and a photo-Nazarov cyclization reaction that deliver the complete nakiterpiosin skeleton efficiently.

Chemistry of 1,3-diarylpropynones in superacids.

In superacids with H0=-14 to -20, it has been found that 1,3-diarylpropynones ArC triple bond CCOAr' are either protonated on oxygen of carbonyl groups with the formation of stable ions ArC triple bond CC(O+H)Ar' or undergo further transformations when the highly conjugated system is electron-rich enough. In the latter case, 3-arylindenones are produced very rapidly and with high efficiency (up to 95% yield in less than 30 min). The influence of the substituents Ar, Ar' and of the reaction conditions on the behavior of 1,3-diarylpropynones and on the intramolecular cyclisation have been studied. From the collected data, a mechanism has been proposed involving vinyl cations ArC+=CHCOAr' and/or dications ArC+=CHC(O+H)Ar'.

Synthesis of novel steroid-tetrahydroquinoline hybrid molecules and D-homosteroids by intramolecular cyclization reactions.

Steroidal aryliminium salts were prepared from D-seco-pregnene aldehyde 2b, and their BF3.OEt2-catalyzed reactions were studied. The nature of the substituent R1 in the anilines 3-6 essentially influenced the chemoselectivity. Using unsubstituted 3, 4-methoxy- (4) or 4-bromoaniline (5), different tetrahydroquinoline derivatives 7a-13a via intramolecular hetero Diels-Alder reaction were formed. In the case of 4-nitroaniline (6) the N-arylamino-D-homopregnane (14a) were also obtained. We assume, that an intramolecular Prins reaction led to this type of fluoro-D-homosteroid. The main products represent a new class of tetrahydroquinolino-androstenes.

Synthesis, X-ray crystal structures and biological activity of 16-amino-17-substituted-D-homo steroid derivatives.

D-Homo derivatives in the androstane and estrane series, 12-19, were synthesized by a fragmentation-cyclization reaction of 16-oximino-17-hydroxy-17-substituted derivatives 3-9, or by cyclization of the corresponding D-seco derivatives 20-26. The structures were confirmed by X-ray analysis of compounds 12 and 16. Preliminary assessment of inhibitory effects of D-homo derivatives from androstane series towards aromatase, 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD), 17 alpha-hydroxylase/C17-20 lyase (P450c17) and 17 beta-HSD indicated much lower inhibitory potential compared to previously tested activity of another type of D-modified steroids, namely D-seco derivatives. Also, assessment of potential antiestrogenic activity of derivatives from estrane series showed absence of such an activity.

Potential antitumor agent: steroidal bilactam ester of p-N, N-bis (2-chloroethyl) aminophenylacetic acid.

7 alpha-, 17 alpha-Diaza-7, 17-dioxo-B, D-dihomo-5-androsten 3 beta-p-N, N-bis (2- chloroethyl)aminophenylacetate, a modified steroidal alkylating agent, is active in the treatment of P388 and L1210 leukemias in vivo. The compound was also tested in vitro against L1210 and P388 leukemias, on DNA, RNA and protein synthesis and showed high inhibition effect. Also increases the frequency of Sister Chromatid Exchanges and reduces the replication index of human lymphocytes.

An efficient procedure for the regiospecific preparation of D-homo-steroid derivatives.

alpha-Diazo-beta-hydroxy esters 3, obtained by condensation of ketones 1 with ethyl diazo(lithio)acetate 2, are efficiently converted into the corresponding beta-ketoesters 4 by exposure to dirhodium (II) tetraacetate. Application of this two-step sequence to 3 beta-acetoxy-5-androstene-17-one 5b and to 3-acetoxy estrone 10b afforded regiospecifically and in very high overall yield the corresponding ethyl 17a-oxo-D-homo-steroid-17-carboxylates 7a,b and 12a,b, which were decarboalkoxylated to give, respectively, 3 beta-hydroxy-D-homo-5-androstene-17a-one 8 and D-homoestrone 13.