Stereoselective synthesis of Certonardolsterol D3

Synthesis and Complete Structure Determination of a Sperm-Activating and -Attracting Factor Isolated from the Ascidian Ascidia sydneiensis

For the complete structure elucidation of an endogenous sperm-activating and -attracting factor isolated from eggs of the ascidian Ascidia sydneiensis ( Assydn-SAAF), its two possible diastereomers with respect to C-25 were synthesized. Starting from ergosterol, the characteristic steroid backbone was constructed by using an intramolecular pinacol coupling reaction and stereoselective reduction of a hydroxy ketone as key steps, and the side chain was introduced by Julia-Kocienski olefination. Comparison of the NMR data of the two diastereomers with those of the natural product led to the elucidation of the absolute configuration as 25 S; thus the complete structure was determined and the first synthesis of Assydn-SAAF was achieved.

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.

Total synthesis and absolute stereochemistry of the proteasome inhibitors cystargolides A and B

The absolute stereochemistry of the cystargolides was determined by total synthesis. Evaluation of synthetic cystargolides and derivatives showed that the natural (2S,3R) stereochemistry is essential for activity. Moreover, benzyl esters (-)-10 and (-)-15 were found to be about 100 times more potent, and to selectively kill MCF-7 cancerous cells.

New Antifungal Cholestane and Aldehyde Derivatives from the Red Alga Laurencia papillosa

The chloroform/methanol extract of the red alga, Laurencia papillosa, collected from the Red Sea in Saudi Arabia, was found to contain two cholestane derivatives: 3α, 6α-dihydroxy-5β-cholestan-12-one (1) and the known, 6β-hydroxycholest-4-en-3-one (2), which was isolated separately in a pure form for the first time. In addition to these compounds, a new aldehyde derivative, ( E)-2-{( E) tridec-2-en-2-yl} heptadec-2-enal (3), was isolated. The structures of all compounds were established based on extensive spectroscopic (1D and 2D NMR, UV, IR) and mass spectrometric studies. All compounds, except 2, were tested for their antifungal activity. Significant activities were associated with 1 and 3 against Candida albicans, Aspergillus fumigatus, and A. flavus.

Access to functionalized steroid side chains via modified Julia olefination

Various functionalized steroidal side chains were conveniently accessed by a modified Julia olefination strategy using a common sulfone donor and an appropriate α-branched aldehyde acceptor. For the coupling of these hindered classes of reaction partners (and in contrast to typically observed trends), the benzothiazolyl(BT)-sulfone anion gave superior outcomes compared to the phenyltetrazolyl(PT)-sulfone anion.

Toxicity of (22R,23R)-22,23-dihydroxystigmastane derivatives to cultured cancer cells

Toxicity of eight 22,23-dihydroxystigmastane derivatives (four pairs of (22R,23R)- and (22S,23S)-isomers differing in steroid backbone structure) to human breast carcinoma MCF-7 cells was compared. For every pair of structurally related compounds, (22R,23R) isomer was found to be significantly more toxic than (22S,23S) isomer. Computational analysis showed that side chain of (22R,23R)-22,23-dihydroxystigmastane derivatives is rigid, whereas that of (22S,23S)-isomers is rather flexible. Structure of steroid backbone significantly affects cytotoxicity of (22R,23R)-22,23-dihydroxystigmastane derivatives to human breast carcinoma MCF-7 cells, human ovary carcinoma CaOv cells, and human prostate carcinoma LnCaP cells. (22R,23R)-3beta,22,23-trihydroxystigmast-5-ene and (22R,23R)-3beta,22,23-trihydroxystigmast-5-en-7-one, both comprising equatorial 3beta-hydroxyl group, exhibited the highest cytotoxicity, while the most polar 28-homobrassinolide and 28-homocastasterone, both comprising 2alpha,3alpha-dihydroxy groups, exhibited the lowest toxicity. Binding of (22R,23R)-22,23-dihydroxystigmastane derivatives to plasmatic membrane was suggested to be important for cytotoxicity.