Design, synthesis and biological evaluation of novel estrone phosphonates as high affinity organic anion-transporting polypeptide 2B1 (OATP2B1) inhibitors.

Organic anion-transporting polypeptide 2B1 (OATP2B1) is a multispecific membrane transporter mediating the cellular uptake of various exo- and endobiotics, including drugs and steroid hormones. Increased uptake of steroid hormones by OATP2B1 may increase tumor proliferation. Therefore, understanding OATP2B1's substrate/inhibitor recognition and inhibition of its function, e.g., in hormone-dependent tumors, would be highly desirable. To identify the crucial structural features that correlate with OATP2B1 inhibition, here we designed modifications at four positions of the estrane skeleton. 13α- or 13ß-estrone phosphonates modified at ring A or ring D were synthesized. Hirao and Cu(I)-catalyzed azide-alkyne click reactions served in the syntheses as key steps. 13ß-Derivatives displayed outstanding OATP2B1 inhibitory action with IC50 values in the nanomolar range (41-87 nM). A BODIPY-13α-estrone conjugate was additionally synthesized, modified at C-3-O of the steroid, containing a four-carbon linker between the triazole moiety and the BODIPY core. The fluorescent conjugate displayed efficient, submicromolar OATP2B1 inhibitory potency. The newly identified inhibitors and the structure-activity relationships specified here promote our understanding about drug recognition of OATP2B1.

Synthesis and evaluation of anticancer activities of 2- or 4-substituted 3-(N-benzyltriazolylmethyl)-13α-oestrone derivatives.

2- or 4-Substituted 3-N-benzyltriazolylmethyl-13α-oestrone derivatives were synthesised via bromination of ring A and subsequent microwave-assisted, Pd-catalysed C(sp2)-P couplings. The antiproliferative activities of the newly synthesised brominated and phosphonated compounds against a panel of human cancer cell lines (A2780, MCF-7, MDA-MB 231) were investigated by means of MTT assays. The most potent compound, the 3-N-benzyltriazolylmethyl-4-bromo-13α-oestrone derivative exerted substantial selective cell growth-inhibitory activity against A2780 cell line with a submicromolar IC50 value. Computational calculations reveal strong interactions of the 4-bromo derivative with both colchicine and taxoid binding sites of tubulin. Disturbance of tubulin function has been confirmed by photometric polymerisation assay.

Focusing on the Catal. of the Pd- and Ni-Catalyzed Hirao Reactions.

The Hirao reaction involving the phosphinoylation or phosphonation of aryl halides by >P(O)H reagents is a P-C bond forming transformation belonging to the recently very hot topic of cross-couplings. The Pd- or Ni-catalyzed variations take place via the usual cycle including oxidative addition, ligand exchange, and reductive elimination. However, according to the literature, the nature of the transition metal catalysts is not unambiguous. In this feature article, the catalysts described for the Pd(OAc)2-promoted cases are summarized, and it is concluded that the "(HOY2P)2Pd(0)" species (Y = aryl, alkoxy) is the real catalyst. In our model, the excess of the >P(O)H reagent served as the P-ligand. During the less studied Ni(II)-catalyzed instances the "(HOY2P)(-OY2P)Ni(II)Cl-" form was found to enter the catalytic cycle. The newest conclusions involving the exact structure of the catalysts, and the mechanism for their formation explored by us were supported by our earlier experimental data and theoretical calculations.

Pd-Catalyzed microwave-assisted synthesis of phosphonated 13α-estrones as potential OATP2B1, 17ß-HSD1 and/or STS inhibitors.

Novel 2- or 4-phosphonated 13α-estrone derivatives were synthesized via the Hirao reaction. Bromo regioisomers (2- or 4-) of 13α-estrone and its 3-benzyl or 3-methyl ether were reacted with diethyl phosphite or diphenylphosphine oxide using Pd(PPh3)4 as catalyst under microwave irradiation. The influence of the new compounds on the transport function of the organic anion transporting polypeptide OATP2B1 was investigated by measuring Cascade Blue uptake. Derivatives bearing a 3-benzyl ether function displayed substantial submicromolar OATP2B1 inhibitory activity. The inhibitory effects of the compounds on human placental steroid sulfatase (STS) and 17ß-hydroxysteroid dehydrogenase type 1 isozyme (17ß-HSD1) were investigated by in vitro radiosubstrate incubation methods. None of the test compounds inhibited the STS markedly. The structure-activity relationship evaluation revealed that 2-substituted 3-hydroxy derivatives are able to inhibit the 17ß-HSD1 enzyme with submicromolar IC50 values. Dual OATP2B1 and 17ß-HSD1 inhibitors have been identified.

New Developments on the Hirao Reactions, Especially from "Green" Point of View.

BACKGROUND: The Hirao reaction discovered ca. 35 years ago is an important P-C coupling protocol between dialkyl phosphites and aryl halides in the presence of Pd(PPh3)4 as the catalyst and a base to provide aryl phosphonates. Then, the reaction was extended to other Preagents, such as secondary phosphine oxides and H-phosphinates and to other aryl and hetaryl derivatives to afford also phosphinic esters and tertiary phosphine oxides. Instead of the Pd(PPh3)4 catalyst, Pd(OAc)2 and Ni-salts were also applied as catalyst precursors together with a number of mono- and bidentate P-ligands. OBJECTIVE: In our review, we undertook to summarize the target reaction with a special stress on the developments attained in the last 6 years, hence this paper is an update of our earlier reviews in a similar topic. CONCLUSIONS: "Greener" syntheses aimed at utilizing phase transfer catalytic and microwave-assisted approaches, even under "P-ligand-free. or even solvent-free conditions are the up-to date versions of the classical Hirao reaction. The mechanism of the reaction is also in the focus these days.