Organoselenium Compounds: Chemistry and Applications in Organic Synthesis.

Selenium, originally described as a toxin, turns out to be a crucial trace element for life that appears as selenocysteine and its dimer, selenocystine. From the point of view of drug developments, selenium-containing drugs are isosteres of sulfur and oxygen with the advantage that the presence of the selenium atom confers antioxidant properties and high lipophilicity, which would increase cell membrane permeation leading to better oral bioavailability. In this article, we have focused on the relevant features of the selenium atom, above all, the corresponding synthetic approaches to access a variety of organoselenium molecules along with the proposed reaction mechanisms. The preparation and biological properties of selenosugars, including selenoglycosides, selenonucleosides, selenopeptides, and other selenium-containing compounds will be treated. We have attempted to condense the most important aspects and interesting examples of the chemistry of selenium into a single article.

Synthesis and biological evaluation of salpichrolide analogs as antiestrogenic agents.

The antiestrogenic activity of three natural salpichrolides A, G and B (1, 3 and 4) and of five synthetic analogs containing an aromatic D ring and a simplified side chain (5-9), was evaluated on MCF-7 cells. The 2,3-ene-1-keto steroids 8 and 9 were obtained from 3ß-acetoxy-17(13→18)-abeo-5αH-pregna-13,15,17-trien-20-one, the key step for these syntheses being a Wharton carbonyl rearrangement of a 1,2-epoxy-3-keto steroid to the allylic alcohol using hydrazine hydrate. The antiestrogenic activity was evaluated by performing dose-response experiments in ER(+) MCF-7 breast cancer cells. Dose-dependent proliferation was quantified via [(3)H]-thymidine incorporation after 3 days treatment. Salpichrolides A, G and B and analogs 5, 8 and 9 were active as antiestrogens with compound 9 being the most active of the synthetic analogs. Compounds 5 and 9 were also evaluated against the ER(-) cell line MDA-MB-231 and shown to be inactive.

Synthesis and antifungal activity of C-21 steroids with an aromatic D ring.

Six analogues of salpichrolides with a simplified side chain (6-11) were synthesized using a new methodology to obtain steroids with an aromatic D-ring. The key step was the elimination of HBr in a vicinal dibromo D-homosteroid by treatment with 1,4-diazabicyclo[2.2.2]octane (DABCO). All new compounds were completely characterized by 2D NMR techniques and tested on two fungal pathogenic species, Fusarium virguliforme and Fusarium solani.

Microwave assisted preparation of C1-C11 oxygen-bridged pregnanes.

1,11-Epoxysteroids may be obtained by an intramolecular remote functionalization using Suarez reagent (diacetoxyiodobenzene/I(2)) and irradiation with visible light. We have found that photolysis with visible light may be advantageously replaced by microwave irradiation to prepare 1,11-oxygen bridges resulting in higher yields and shorter reaction times especially in the case of sensitive substrates. Both methodologies were compared on a set of representative 11-α-hydroxypregnanes (3, 8, 10 and 11).

Synthesis of 6,19-cyclopregnanes. Constrained analogues of steroid hormones.

A procedure for the synthesis of 6,19-cyclopregnanes is described involving an intramolecular alkylation reaction of Delta(4)-3-keto steroids with a 19-mesylate in the presence of KOH in isopropanol. Three 6,19-cyclopregnanes were prepared (4, 5 ,9); in the rat, 6,19-cycloprogesterone (4) and its 21-hydroxy derivative 5 displaced [3H]-dexamethasone from glucocorticoid receptors, the former compound being more active. Both compounds did not compete with [3H]-aldosterone for kidney mineralocorticoid receptors nor with [3H]-R5020 for uterus progesterone receptors.