Synthesis of Alkaloid Demissidine Stereoisomers and Analogues.

Demissidine is an indolizidine alkaloid isolated from several potato species. A simple synthesis of demissidine stereoisomers and analogues from a common steroidal sapogenin tigogenin is presented in the paper. The key intermediate in the synthesis of these compounds is readily available tigogenoic acid.

Identification of Essential Residues for Ciprofloxacin Resistance of Ciprofloxacin-Modifying Enzyme (CrpP) of pUM505.

The ciprofloxacin-resistance P gene, encoded by the pUM505 plasmid, isolated from a clinical isolate, confers an enzymatic mechanism of antibiotic phosphorylation, which is ATP-dependent, that decreases ciprofloxacin susceptibility. Homologous P genes are distributed across extended spectrum beta-lactamase (ESBL)-producing isolates obtained from Mexican hospitals and which confer decreased susceptibility to CIP. The analysis of sequences of the CrpP of proteins showed that the residues Gly7, Thr8, Asp9, Lys33 and Gly34 (located at the -terminal region) and Cys40 (located at the C-terminal region) are conserved in all proteins, suggesting that these residues could be essential for CrpP function.

TiCl catalyzed cleavage of (25R)-22-oxo-23-spiroketals. Synthesis of sapogenins with furostanol and pyranone E rings on the side chain.

The regioselective opening of the F ring of 22-oxo-23-spiroketals 7a-d using TiCl in acetic anhydride yielded the novel furostanols 11a-d along with cholestanic derivatives 8a-d with pyranone E ring. The structures of the new derivatives thus obtained were established using one- (DEPT) and two-dimensional H, C NMR experiments (COSY, HSQC, HMBC, NOESY). The 22α-hydroxyl orientation in compounds 11a-d was proposed by comparison of the C chemical shifts with those of other aglycone members of this family, and confirmed by combined NOESY and X-ray diffraction analysis of compound 11a.

Synthesis of bis(indolyl)methanes Catalyzed by Triethylborane.

Triethylborane (TEB) was found to be a mild, efficient, and acid catalyst in electrophilic substitution reaction of indoles with aldehydes compounds to afford the corresponding bis(indolyl)methanes. Vibrindole and bis(indolyl)methanes derivatives and were synthesized using this methodology. Compound is an intermediary in the synthesis of the natural bisindoles arsindoline and streptindole .

Regio- and stereoselective cleavage of steroidal 22-oxo-23-spiroketals catalyzed by BF3·Et2O.

The regioselective opening of the F ring of 22-oxo-23-spiroketals using BF3·OEt2 in acetic anhydride yielded novel cholestanic frameworks with pyranone E ring 20-23. The structures of the new derivatives of botogenin, diosgenin, hecogenin and tigogenin thus obtained were established using one and two dimensional (1)H, (13)C experiments (DEPT, COSY, HETCOR, HMBC). The X-ray diffraction analysis unequivocally confirmed the R configuration at C-23 in the starting 22-oxo-23-spiroketal 18 and the Z configuration of the C23-C24 double bond in the reaction product 20.

Crystal structure of N-[(E)-(1,3-benzodioxol-5-yl)-methyl-idene]-4-chloro-aniline.

In the title compound, C14H10ClNO2, obtained by the condensation of 4-chloro-aniline and piperonal, the five-membered ring is almost planar (r.m.s.

O-Ethyl S-{(S)-1-oxo-1-[(R)-2-oxo-4-phenyl-oxazolidin-3-yl]propan-2-yl} carbonodi-thio-ate.

In the title compound, C15H17NO4S2, synthesized by addition of O-ethylxanthic acid potassium salt to a diastereomeric mixture of (4R)-3-(2-chloro-propano-yl)-4-phenyl-oxazolidin-2-one, the oxazolidinone ring has a twist conformation on the C-C bond. The phenyl ring is inclined to the mean plane of the oxazolidinone ring by 76.4 (3)°.

(25R)-16β-Acet-oxy-3β-bromo-23',26-ep-oxy-23',25-dimethyl-5α-cholest-23,23'-en-6-one dichloro-methane monosolvate.

The crystal structure of the title compound, C31H45BrO5·CH2Cl2, prepared in six steps from diosgenin, confirmed that the configurations of the stereogenic centers, positions 20S and 25R, remain unchanged during the reaction. The six-membered A, B and C rings have chair conformations. The five-membered ring D has an envelope conformation (with the methyl-substituted C atom fused to ring C as the flap) and the six-membered dihydro-pyran ring E adopts a twist-boat conformation.

Regioselective cleavage of 22-oxo-23-spiroketals. Novel cholestanic frameworks with pyranone and cyclopentenone E rings on the side chain.

The regioselective opening of the F ring of 22-oxo-23-spiroketals using a saturated solution of HCl in acetic anhydride yielded novel cholestanic frameworks with pyranone or cyclopentenone E rings. The structures of the new derivatives of sarsasapogenin, diosgenin and hecogenin thus obtained were established using one and two dimensional (1)H, (13)C experiments (DEPT, COSY, HETCOR, HMBC, ROESY, and NOESY). The X-ray analysis for compound 11b confirmed the 23R configuration for the new stereogenic center.

Mechanistic insights and new products of the reaction of steroid sapogenins with NaNO2 and BF3.Et2O in acetic acid.

A detailed analysis of the course of the reaction of steroid sapogenins with NaNO(2) and BF(3).Et(2)O in acetic acid is presented and some evidences on the involved mechanism are provided. Two new products of the studied reaction were isolated and unambiguously characterized with the aid of NMR and single crystal X-ray diffraction.

Synthesis of "glycospirostanes"--steroid sapogenins with a sugar-like ring F.

The synthesis of two "glycospirostanes" from 23-oxotigogenin acetate is described. (23S,24S,25R)-5alpha-Spirostane-3beta,23,24,25-tetraol was obtained by dehydrogenation followed by stereoselective reduction of the 23-oxo group and OsO(4) dihydroxylation of the C24-C25 double bond. Allylic hydroxylation with SeO(2) of 3beta-acetoxy-5alpha-spirost-23-ene obtained from 23-oxotigogenin acetate followed by OsO(4) dihydroxylation of the C23-C24 double bond afforded (23R,24S,25R)-5alpha-spirostane-3beta,23,24,25-tetraol.

New bisfuran derivative from sarsasapogenin. An X-ray and NMR analysis.

The new bisfuran derivative, (22S,23S)-22,23-dihydroxy-23,26-epoxyfurostane, was obtained from the known oxidation of sarsasapogenin acetate with NaNO2/BF3 in 5% aqueous acetic acid. The structure of was established using one and two-dimensional 1H, 13C experiments (DEPT, COSY, HETCOR and HMBC) and the configurations at the newly formed stereogenic centers were established as 22S,23S by an X-ray diffraction analysis. Addition of TiCl4 to bisfuran 5 confirmed that this compound is an intermediate in the rearrangement to 22-oxo-23-spiroketals since it was transformed quantitatively into the latter product.