Bohumil Steiner

Preparation and crystal and molecular structure of 6-O-[(2S)-2,3-epoxypropyl]-1, 2:3,4-di-O-isopropylidene-α-d-galactopyranose. Pyranoid ring conformation in 1,2:3,4-di-O-isopropylidene galactopyranose and related systems

Abstract The title compound was isolated by several recrystallisations from a 1:1 mixture of diastereomers which was obtained in 75% yield from the reaction of 1,2:3,4-di-O- isopropylidene-α- d -galactopyranose with epichlorohydrin. The absolute configuration of this isomer (30% yield) was established by X-ray crystallography. The conformation of the pyranoid ring in this compound is compared to those in related situations. In all these cases the pyranoid ring adopts a heavily distorted conformation which is described on average as between the screw-boat OS5 and the twist-boat (“skew”-boat) OT2 with deviations in the direction of the boat B2,5 in most cases. The puckering parameters for all such reported pyranoid rings were calculated or recalculated, and are given within expanded conventions of carbohydrate nomenclature.

Cyclodextrin derivative of hyaluronan

Conversion of hyaluronan (HA) to its β-cyclodextrin derivative (HA-β-CD) was accomplished by direct coupling of β-cyclodextrin (β-CD) molecules with carboxylic acid groups of the HA macromolecule. The intermolecular dehydration, yielding the HA-β-CD derivative, was performed by the action of diethyl azodicarboxylate and triphenylphosphine under mild, neutral conditions. The physico-chemical characteristics of the novel (bio)material, determined both in solution and solid state, were compared with those of native HA. The specific action of a hyaluronidase was exploited to advantage in studying the depolymerization kinetics of the two types (HA and HA-β-CD) of macrobiomolecules.

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

Abstract Application of the Strecker reaction to methyl 6-deoxy-2,3- O -isopropylidene- α - l - lyxo -hexopyranosid-4-ulose resulted in the formation of methyl 4-amino-4-cyano-4,6-dideoxy-2,3- O -isopropylidene- α - l -talopyranoside, methyl 4-amino-4-cyano-4,6-dideoxy-2,3- O -isopropylidene- β - d -allopyranoside and methyl 4-cyano-6-deoxy-2,3- O -isopropylidene- α - l -talopyranoside. Their proportionality and yields depend on the reaction conditions used. Additionally, 4-amino-4-cyano-4,6-dideoxy-2,3- O -isopropylidene- α - l -talopyranoside can be prepared favourably from preformed methyl 4-cyano-6-deoxy-2,3- O -isopropylidene- α - l -talopyranoside. The crystal structure of methyl 4-acetamido-4-cyano-4,6-dideoxy-2,3- O -isopropylidene- α - l -talopyranoside is also presented.

An efficient and versatile synthesis of apiose and some C-1-aldehyde- and/or 2,3-O-protected derivatives

Abstract The synthesis of 2,3- O -isopropylidene-β- d -apiofuranose (58% overall yield) from l -arabinose via 3- C -(hydroxymethyl)-2,3- O -isopropylidene- d - glycero -tetrose diethyl dithioacetal is reported. Starting from l -arabinose an alternative precursor of d -apiose, 3- C -(hydroxymethyl)-2,3- O -isopropylidene- d - glycero -tetrose dimethyl acetal, was prepared from 2,3- O -isopropylidene- l - threo -tetrodialdose dimethyl acetal and formaldehyde by the aldol-Cannizzaro reaction. Unprotected d -apiose is accessible from both precursors on acid hydrolysis.

Reaction of selected carbohydrate aldehydes with benzylmagnesium halides: benzyl versus o-tolyl rearrangement

Summary The Grignard reaction of 2,3-O-isopropylidene-α-D-lyxo-pentodialdo-1,4-furanoside and benzylmagnesium chloride (or bromide) afforded a non-separable mixture of diastereomeric benzyl carbinols and diastereomeric o-tolyl carbinols. The latter resulted from an unexpected benzyl to o-tolyl rearrangement. The proportion of benzyl versus o-tolyl derivatives depended on the reaction conditions. Benzylmagnesium chloride afforded predominantly o-tolyl carbinols while the application of benzylmagnesium bromide led preferably to the o-tolyl carbinols only when used in excess or at higher temperatures. The structures of the benzyl and o-tolyl derivatives were confirmed unambiguously by NMR spectral data and X-ray crystallographic analysis of their 5-ketone analogues obtained by oxidation of the corresponding mixture of diastereomeric carbinols. A possible mechanism for the Grignard reaction leading to the benzyl→o-tolyl rearrangement is also proposed.

6-O-Cyanomethyl-1,2:3,4-di-O-isopropylidene-α-D-galactopyranose

The analysis of the title compound, C14H21NO6, revealed a highly distorted conformation of the six-membered pyranose ring. The presence of two five-membered 1,3-dioxolane rings fused to the pyranose ring at the 1,2- and 3,4-positions is responsible for the severe deviation from the usual chair conformation of the pyranose ring. The three-dimensional packing is stabilized by weak hydrogen bonds of the C-H...O type.

Some amino sugars structurally related to 6-deoxymannojirimycin precursors prepared from methyl 6-deoxy-2,3-O-isopropylidene-α-d-lyxo-hexofuranosid-5-ulose and methyl 2,3-O-isopropylidene-α-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.

Crystal Structure of Methyl 4-amino-4-cyano-4,6-dideoxy-2,3- O-isopropylidene-α -L-talopyranoside

The detailed structure of methyl 4-acetamido-4-cyano-4,6-dideoxy-2,3Oisopropylideneβ-D-allopyranoside was established by X-ray analysis confirming allo configuration at C-4 and suggesting a C1 conformation of the pyranose ring. The values of relevant torsion angles and calculated puckering parameters revealed a distortion into the direction of H5, thus indicating a flattening at C-1 and C-4.

(4R)-1'-Acetyl-2,3-O-isopropylidene-methylspiro [4,6-dideoxy-ß-D-ribo-hexopyranosid-4,5'-imidazolidin]-2',4'-dione

Acetylation of hydantoins (imidazolidin-2,4-diones) and their 5-substituted derivatives normally occurs more readily in the 1-position [1].[...]

2,3:4,6-Di- O -isopropylidene-α-L-sorbofuranose and 2,3- O -isopropylidene-α-L-sorbofuranose

In the title compounds, C(12)H(20)O(6), (I), and C(9)H(16)O(6), (II), the five-membered furanose ring adopts a (4)T(3) conformation and the five-membered 1,3-dioxolane ring adopts an E(3) conformation. The six-membered 1,3-dioxane ring in (I) adopts an almost ideal (O)C(3) conformation. The hydrogen-bonding patterns for these compounds differ substantially: (I) features just one intramolecular O-H...O hydrogen bond [O...O = 2.933 (3) A], whereas (II) exhibits, apart from the corresponding intramolecular O-H...O hydrogen bond [O...O = 2.7638 (13) A], two intermolecular bonds of this type [O...O = 2.7708 (13) and 2.7730 (12) A]. This study illustrates both the similarity between the conformations of furanose, 1,3-dioxolane and 1,3-dioxane rings in analogous isopropylidene-substituted carbohydrate structures and the only negligible influence of the presence of a 1,3-dioxane ring on the conformations of furanose and 1,3-dioxolane rings. In addition, in comparison with reported analogs, replacement of the -CH(2)OH group at the C1-furanose position by another group can considerably affect the conformation of the 1,3-dioxolane ring.