Stereocontrolled synthesis of steroid side chains via organoboranes. Stereospecific synthesis of 20R- and 20S-25-hydroxycholesterol.

Both 20R- and 20S-25-hydroxycholesterol have been stereospecially prepared from readily 3β-hydroxy-5-androsten-17-one.     

A new synthesis of 25-hydroxycholesterol

A simple (η³-allyl)palladium-based synthesis of 25-hydroxycholesterol is described using a dimetallated coupling reagent.     

Stereocontrolled synthesis of an indole moiety of sespendole and stereochemical assignment of the side chain

Two possible diastereomers of the indole moiety of sespendole were synthesized from 3-hydroxy-4-nitrobenzaldehyde in a highly stereoselective manner. Comparison of (1)H and (13)C NMR spectra of the two synthetic materials with those sespendole leads us to propose that the relative stereochemistry of the epoxyalcohol is syn.     

Synthetic studies on neomarinone: practical and efficient stereoselective synthesis of the side chain

A practical and efficient stereoselective synthesis of the side chain of neomarinone is reported. The synthesis was achieved in six steps (41% overall yield) from 2-methyl-2-cyclohexenone. The key step is a novel stereoselective 1,4-conjugate addition/enolate alkylation by an epoxide-opening reaction.     

Regio and stereochemically controlled ring opening of epoxides with grignard reagents. Stereocontrolled synthesis of the steroid side chains. first stereoselective hemisynthesis of 20s isolanosterol.

Title compound was efficiently prepared taking advantage of a stereoselective hydride shift during the reaction between the Grignard reagent derived from ethoxyacetylene and an epoxide. The solvent was found to have a crucial role in this and related reactions.     

Stereocontrolled syntheses of alpha-C-mannosyltryptophan and its analogues

The total synthesis of alpha-C-mannosyltryptophan (C-Man-Trp), a naturally occurring C-glycosylamino acid, was achieved from a commercially available alpha-methyl-D-mannoside in 10 steps including the following key steps: the C-glycosidation of a mannose derivative with a stannylacetylene, Castro indole synthesis, and Sc(ClO4)3-promoted coupling with L-serine-derived aziridine carboxylate. The glucose- and galactose-analogues of C-Man-Trp were also synthesized in a similar manner. Conformational analyses of the synthesized C-glycosyltryptophan and its synthetic intermediate are briefly discussed.     

A concise and stereoselective synthesis of the brassinolide and related compounds’ side chains

A stereoselective synthesis of brassinolide, which involves construction of the side chain by highly stereoselective aldol reaction of 20S-6β-methoxy-3α,5-cyclo-5α-pregnane-20-carboxadehyde 5 with the anion of α-silyloxy ketone 6 is described.     

An approach to stereoselective formation of glycinoeclepin a side chain

Claisen rearrangement was found to be an efficient method for the stereoselective construction of the glycinoeclepin A side chain.     

Stereoselective synthesis of 25-hydroxyvitamin D2 side chain via the acetal template route

A highly stereoselective synthesis of the side chain of 25-hydroxyvitamin D₂ and 1α,25-dihydroxyvitamin D₂ is described.     

Stereocontrolled synthesis and determination of the c-24 and 25 stereochemistry of glaucasterol

(24S,25S)- and (24R,25R)-24,26-Cyclocholesta-5,22E-dien-3β-ols (1a and 1b) were synthesized stereoselectively. Their ₁H NMR comparison with natural glaucasterol (1) allowed to conclude that 1 possesses 24S,25S stereochemistry.     

Stereocontrolled syntheses of carbocyclic C-nucleosides and related compounds.

Carbocyclic 9-deazapurine nucleosides (1-4), a spiranic pyrimidone carbocyclic compound (5), and an unusual carbocyclic isonucleoside (6) were prepared as enantiomerically pure compounds via the key intermediates 10 and 21 from 1,4-gamma-ribonolactone. The key intermediate 10 was prepared by stereoselective reduction with Bu3SnH and then converted to carbocyclic C-ribonucleosides 1, 3, and 4. 2',3'-Didehydro-2',3'-dideoxycarbocyclic 9-deazainosine (2) was prepared from a 2',3'-dimesylate 17 by treatment with Li2Te followed by an acidic deprotection. The key bicyclic intermediate 21 was prepared from a diol 20 by an intramolecular cyclization using CHI3-Ph3P-imidazole and converted to the spiranic compound 5 and an olefinic nucleoside 6 by the construction of the heterocyclic moiety followed by deprotection.