Biomedical subjects

Vratislav Langer

Publications and source records attributed to Vratislav Langer.

24 records · Page 2Linked to original sources

PubMed2004

Dirubidium aquapentachlorochromate(III) and dicaesium aquapentachlorochromate(III).

The structures of the two novel title compounds, Rb(2)[CrCl(5)(H(2)O)], (I), and Cs(2)[CrCl(5)(H(2)O)], (II), have been determined by single-crystal X-ray diffraction. Compounds (I) and (II) crystallize with Pnma and Cmcm symmetry, respectively. In (I), the Cr, three Cl and water O atom lie on a mirror plane; in (II), the Cs, Cr, O and one of the Cl atoms are at sites with m2m symmetry. The chromate anions are in a pseudo-cubic environment of eight Rb(+) cations in (I) and in a pseudo-octahedral environment of six Cs(+) cations in (II). The structural arrangement correlates with the r(anion)/r(cation) radius ratio.

Journal Article↗

PubMed2003

Characterisation and X-ray crystallography of products from the Bucherer-Bergs reaction of methyl 2,3-O-isopropylidene-alpha-D-lyxo-pentodialdo-1,4-furanoside.

Methyl 2,3-O-isopropylidene-alpha-D-mannofuranosidurononitrile [alternative name: methyl (5R)-5-C-cyano-2,3-O-isopropylidene-alpha-D-lyxofuranoside] (2), methyl 2,3-O-isopropylidene-alpha-D-mannofuranosiduronamide [methyl (5S)-5-C-carbamoyl-2,3-O-isopropylidene-alpha-D-lyxofuranoside; methyl (5S)-2,3-O-isopropylidene-alpha-D-lyxo-hexofuranosiduronamide] (3), methyl 2,3-O-isopropylidene-alpha-D-mannofuranosiduronic acid [methyl (5S)-2,3-O-isopropylidene-alpha-D-lyxo-hexofuranosiduronic acid] (4), methyl 5-deoxy-2,3-O-isopropylidene-5-ureido-beta-L-gulofuranosiduronamide [methyl (5R)-5-deoxy-2,3-O-isopropylidene-5-ureido-alpha-D-lyxo-hexofuranosiduronamide (5), and (4S,5S,6R)-5,6-dihydro-6-hydroxy-4,5-isopropylidenedioxy-4H-pyrido[2,1-e]imidazolidine-2',4'-dione [IUPAC name: (3aS,4R,8aS)-4-hydroxy-2,2-dimethyl-3a,8a-dihydro-4H-1,3-dioxa-4a,6-diaza-s-indacene-5,7-dione] (6), instead of the expected hydantoin derivative, were obtained from the Bucherer-Bergs reaction of methyl 2,3-O-isopropylidene-alpha-D-lyxo-pentodialdo-1,4-furanoside (1). The structure of 6 was deduced from NMR and mass spectral data and confirmed by X-ray crystallography. The configuration at C-5 in 2-5 was confirmed by establishing the 5S configuration of 3 by X-ray crystallography. Conformations of the six- and five-membered rings in 3 and 6 are also discussed.

Carbohydrate Conformation↗

PubMed2003

Some non-anomerically C-C-linked carbohydrate amino acids related to leucine-synthesis and structure determination.

(5'R)-5'-Isobutyl-5'-[methyl (4R)-2,3-O-isopropylidene-beta-L-erythrofuranosid-4-C-yl]-imidazolidin-2',4'-dione was synthesised starting from methyl 2,3-O-isopropylidene-alpha-D-lyxo-pentodialdo-1,4-furanoside via methyl 6-deoxy-6-isopropyl-2,3-O-isopropylidene-alpha-D-lyxo-hexofuranosid-5-ulose applying the Bucherer-Bergs reaction. Its 5'-R configuration was confirmed by X-ray crystallography. Corresponding alpha-amino acid-methyl (5R)-5-amino-5-C-carboxy-5,6-dideoxy-6-isopropyl-alpha-D-lyxo-hexofuranoside (alternative name: 2-[methyl (4R)-beta-L-erythrofuranosid-4-C-yl]-D-leucine) was obtained from the above hydantoin by acid hydrolysis of the isopropylidene group followed by basic hydrolysis of the hydantoin ring. Analogous derivatives with 5S configuration, formed in a minority, were also isolated and characterised.

Amino Sugars↗

PubMed2002

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.

1-Deoxynojirimycin↗

PubMed2002

Chiral 2,2'-bipyridine-type N-monoxides as organocatalysts in the enantioselective allylation of aldehydes with allyltrichlorosilane.

[reaction: see text] The Sakurai-Hosomi-type allylation of aromatic and heteroaromatic aldehydes can be catalyzed by the new heterobidenate bipyridine monoxide PINDOX with high enantioselectivities. The sterochemical outcome is mainly controlled by the axial chirality in PINDOX, which in turn is determined by the annulated terpene units.

Journal Article↗

PubMed1999

An Approach toward the Triquinane-Type Skeleton via Reagent-Controlled Skeletal Rearrangements. A Facile Method for Protection-Deprotection of Organomercurials, Tuning the Selectivity of Wagner-Meerwein Migrations, and a New Route to Annulated Lactones.

Nonlinear triquinane-type building blocks have been synthesized using three strategic steps, namely, (1) Hg(2+)-mediated opening of a cyclopropane ring involving a skeletal rearrangement (3 --> 8), (2) an intramolecular organometallic addition across a C=O bond triggered by activation of the C-HgX group by means of Me(3)CuLi(2) (14 --> 26), and (3) selective, reagent-controlled skeletal rearrangements (43 --> 47 with Tl(3+) or Hg(2+); 43 --> 51 + 52 with Pd(2+); 44 --> 47 with Pd(2+)). A new method for protection/deprotection of organomercurials has been developed, which allows selective reduction of a carbonyl group with NaBH(4) and other hydrides (8 --> 14 --> 16 --> 20) and Tebbe methylenation (14 --> 31 --> 32). Oxidative demercuration (8 --> 11 + 28) and Pd(2+)-catalyzed carbonylation of organomercurials (20 --> 53) allowed syntheses of gamma- and delta-lactones.

Journal Article↗