Access to functionalized steroid side chains via modified Julia olefination

New selenosteroids as antiproliferative agents

Starting from natural steroids (diosgenin, hecogenin, smilagenin, estrone), we have prepared a wide panel of selenoderivatives, including benzoselenazolones, selenosemicarbazones, isoselenocyanates, selenoureas, selenocyanates and diselenides, with the aim of developing new families of potential chemotherapeutic agents. The modification of the organoselenium moieties, and their position on the steroid provided valuable information concerning the antiproliferative activities. Among all the families accessed herein, the best profile was achieved for selenoureas on the A ring of estrone, which exhibited GI₅₀ values in the range 2.0-4.1 μM for all the tested tumor cell lines, with increased potency compared with commonly used chemotherapeutic agents, like 5-fluorouracil and cisplatin. Cell cycle analysis revealed that selenoureas induced accumulation of cells in the G₁ phase of the cell cycle in the breast cancer cell lines HBL-100 and T-47D; therefore, a different mechanism than cisplatin, that induces cell cycle accumulation in the S phase as a result of DNA damage, must be involved. In the rest of the tumor cells, a slight increase of the S compartment was observed. Moreover, selenosteoids turned out to be excellent glutathione peroxidase (GPx) mimics for the catalytic removal of deleterious H₂O₂ (t_1/2 8.0-22.5 min) and alkyl peroxides (t_1/2 23.0-38.9 min) when used in substoichiometric amounts (1% molar ratio), thus providing a valuable tool for reducing the intrinsic oxidative stress in tumor progression.

Total Synthesis of Linckosides A and B, the Representative Starfish Polyhydroxysteroid Glycosides with Neuritogenic Activities

Linckosides A and B, two starfish metabolites with promising neuritogenic activities, are synthesized in a longest linear sequence of 32 steps and 0.5% overall yield; this represents the first synthesis of members of the polyhydroxysteroid glycoside family, which occur widely in starfishes.

Crotylboron-based synthesis of the polypropionate units of chaxamycins A/D, salinisporamycin, and rifamycin S

Syntheses of the C(15)-C(27) fragments of chaxamycins A/D, rifamycin S, and the C(12)-C(24) fragment of salinisporamycin have been accomplished in 10 steps from commercially available starting materials. Three crotylboron reagents were utilized to construct the seven contiguous stereocenters in these fragments with excellent stereoselectivity.

Substrate analog studies of the ω-regiospecificity of Mycobacterium tuberculosis cholesterol metabolizing cytochrome P450 enzymes CYP124A1, CYP125A1 and CYP142A1

We report the synthesis and evaluation of a series of cholesterol side-chain analogs as mechanistic probes of three important Mycobacterium tuberculosis cytochrome P450 enzymes that selectively oxidize the ω-position of the methyl-branched cholesterol side-chain. To probe the structural requirements for the thermodynamically disfavored ω-regiospecificity we compared the binding of these substrate analogs to each P450, determined the turnover rates, and characterized the enzymatic products. The results are discussed in the context of the structure-activity relationships of the enzymes and how their active sites enforce ω-oxidation.