4-Amino-4-cyano-4,6-dideoxy sugar derivatives from methyl 6-deoxy-2,3-O-isopropylidene-α-l-lyxo-hexopyranosid-4-ulose via Strecker-type reaction

Rietveld refinement with wavelet compressed data sets

Crystal structures of highly ordered triclinic kaolinite, cubic hexamethylentetramine and a part of the structure of monoclinic rare sugar were refined by Rietveld method using wavelet compressed sets of intensities. Compression of intensities sets was accomplished by a discrete wavelet transform (DWT). It was found that accuracy of refined positional parameters did not change significantly even if the compression ratio reached 8:1. Similarly, quantitative phase analysis done by Rietveld method provided very close estimates of phase composition for compression ratios 2:1 and 4:1.

Application of DWT compressed data led to time savings approaching 50–60% without significant loss of information. This procedure may accelerate molecular modelling based on powder data, or speed up introductory steps of Rietveld refinements with extensive data/parameters sets.

Prediction of crystal structure of a rare monosaccharide – influence of model geometry

Crystal structure of a hexagonal monosaccharide, C11H18N2O4, was succesfully predicted by potential energy minimisation. Four starting molecular models differing in ring conformations were based on similar structures and the positions of two substituents (-NH2, -CN) were found by semiempirical AM1 calculations. Generated structures were ranked according to both potential energy values and corre-sponding Rwp ´s. Calculated potential energy was sensitive to changes in the geometries of the sachcharide rings as well as to the positions of substituents. Rigid body Rietveld refinements did not improve accuracy of the crystal structures with low Rwp ´s and high potential energy.

Prediction of crystal structures of two monosaccharides by potential energy minimisation

Crystal structures of a monoclinic and a hexagonal monosaccharide, 40 atoms per molecule, were successfully predicted by a potential energy minimisation method. The intermolecular interactions were described by three terms covering electrostatic, attraction and repulsion contributions to the total energy. Two types of atomic charges based on the Hartree-Fock wave function, Mulliken and derived from the electrostatic field generated by a molecule, were combined with two force fields called Williams and Dreiding. With the cell parameters fixed, the correct structure was found in approximately 75 % of cases. With the cell parameters optimised no reasonable structure was found for the hexagonal monosaccharide. The accuracy of the predicted structures was evaluated by means of X-ray Rietveld refinements.

Highly Diastereoselective Cyanation of Methyl Ketimines Obtained from (R)-Glyceraldehyde

[reaction: see text] Addition of trimethylsilyl cyanide to ketimines derived from (R)-2,2-dimethyl-1,3-dioxolan-4-yl methyl ketone to generate a quaternary stereocenter has been achieved with high yields and excellent diastereoselectivity. The stereoselectivity was found to be temperature and solvent dependent. The beta-hydroxy-alpha-amino nitrile of syn configuration was the major compound in kinetically controlled reactions, whereas the anti stereoisomer was obtained in excess in thermodynamically controlled reactions. Double stereodifferentiation under kinetic control conditions was successful, and the cyanation reaction occurred with complete syn diastereoselectivity using the matched pair. The versatility of the resulting amino nitrile as a synthetic intermediate was tested by performing the synthesis of orthogonally protected (R)-(2-aminomethyl)alanine.

First Synthesis and Evaluation of the Inhibitory Effects of Aza Analogues of TSAO on HIV-1 Replication

Aza TSAO-T derivatives bearing a dihydroisothiazole dioxide ring instead of an oxathiole dioxide ring at the C-3' position on the sugar moiety were prepared. We have synthesized four families of compounds depending on substitution at both N-3 and N-2' '. Biological evaluation showed that these compounds are HIV-1(III(B))-specific and potent reverse transcriptase inhibitors with EC(50) values between 0.13 and 3.5 microM in cell culture.

Synthesis of 4-Amino-5-H-2,3-dihydroisothiazole-1,1-dioxide Ring Systems on Sugar Templates via Carbanion-Mediated Sulfonamide Intramolecular Cyclization Reactions (CSIC Protocols) of Glyco-α-sulfonamidonitriles

The carbanion-mediated sulfonate intramolecular cyclizations (CSIC protocols) of glyco-alpha-sulfonamidonitriles derived from readily available monosaccharides have been extensively investigated using potassium carbonate, cesium carbonate, n-BuLi, and LDA as bases. As a result, a series of enantiomerically pure spiro(4-amino-5-H-2,3-dihydroisothiazole-1,1-dioxide) derivatives have been prepared efficiently and isolated in good yield. The synthesis of these new bicyclic systems is key to accessing a novel range of aza analogues of TSAO nucleosides (ATSAOs).

Synthesis, Crystal Structure, and Conformation of Methyl 5-Oacetyl-5-cyano-6-deoxy-2,3-O-isopropylidene-β-L-gulofuranoside

Methyl 5-O-acetyl-5-cyano-6-deoxy-2,3-O-isopropylidene-β-l-gulofuranoside was prepared in high yield from methyl 6-deoxy-2,3-O-isopropylidene-α-d-lyxo-pentodialdo-1,4-furanoside. The configuration at the C5 atom was unambiguosly established by single crystal X-ray analysis of the corresponding 5-O-acetyl derivative. The conformation of the furanose and 1,3-dioxolane rings is also discussed.

Some amino sugars structurally related to 6-deoxymannojirimycin precursors prepared from methyl 6-deoxy-2,3-O-isopropylidene-alpha-D-lyxo-hexofuranosid-5-ulose and methyl 2,3-O-isopropylidene-alpha-D-lyxo-pentodialdo-1,4-furanoside

Methyl (5S)-5-C-amino-5-cyano-5-deoxy-2,3-O-isopropylidene-alpha-D-lyxofuranoside has been synthesised from methyl 2,3-O-isopropylidene-alpha-D-lyxo-pentodialdo-1,4-furanoside, applying the Strecker synthesis. Analogously, methyl (5S) and (5R)-5-C-amino-5-cyano-5,6-dideoxy-2,3-O-isopropylidene-alpha-D-lyxo-hexofuranosides were prepared from methyl 6-deoxy-2,3-O-isopropylidene-alpha-D-lyxo-hexofuranosid-5-ulose. The 5-S configuration was unambiguously determined by single-crystal X-ray diffraction analysis of corresponding N-acetyl derivatives. Conformations of five-membered rings are discussed. The conversion of N-acetylated amino nitriles to N-acetylamino acid ethyl ester and amide, respectively, is also described.

Preparation and structure determination of two sugar amino acids via corresponding hydantoin derivatives

(4R)-2,3-O-Isopropylidene-methylspiro[4,6-dideoxy-alpha-L-lyxo+ ++-hexopyranosid-4,5'-imidazolidin]-2',4'-dione and (4R)-2,3-O-isopropylidene-methylspiro[4,6-dideoxy-beta-D-ribo-h exopyranosid-4,5'-imidazolidin]-2',4'-dione were prepared under various reaction conditions starting from methyl 6-deoxy-2,3-O-isopropylidene-alpha-L-lyxo-hexopyranosid-4-++ +ulose. Corresponding alpha-amino acids methyl (4R)-4-amino-4-C-carboxy-4,6-dideoxy-alpha-L-lyxo-hexopyranosid e and methyl (4R)-4-amino-4-C-carboxy-4,6-dideoxy-beta-D-ribo-hexopyranoside were obtained from the above hydantoins by selective acid hydrolysis of the isopropylidene group, followed by basic hydrolysis of the hydantoin ring. The crystal structures of both hydantoin derivatives are also presented.