The Bucherer-Bergs Multicomponent Synthesis of Hydantoins-Excellence in Simplicity.

Hydantoins and their hybrids with other molecules represent a very important group of heterocycles because they exhibit diverse biological and pharmacological activities in medicinal and agrochemical applications. They also serve as key precursors in the chemical or enzymatic synthesis of significant nonnatural α-amino acids and their conjugates with medical potential. This review provides a comprehensive treatment of the synthesis of hydantoins via the Bucherer-Bergs reaction including the Hoyer modification but limited to free carbonyl compounds or carbonyl compounds protected as acetals (ketals) and cyanohydrins used as starting reaction components. In this respect, the Bucherer-Bergs reaction provides an efficient and simple method in the synthesis of important natural products as well as for the preparation of new organic compounds applicable as potential therapeutics. The scope and limitations, as well as a comparison with some other methods for preparing hydantoins, are also discussed.

Synthesis of 1,4-imino-L-lyxitols modified at C-5 and their evaluation as inhibitors of GH38 α-mannosidases.

A synthetic approach to 1,4-imino-L-lyxitols with various modifications at the C-5 position is reported. These imino-L-lyxitol cores were used for the preparation of a series of N-(4-halobenzyl)polyhydroxypyrrolidines. An impact of the C-5 modification on the inhibition and selectivity against GH38 α-mannosidases from Drosophila melanogaster, the Golgi (GMIIb) and lysosomal (LManII) mannosidases and commercial jack bean α-mannosidase from Canavalia ensiformis was evaluated. The modification at C-5 affected their inhibitory activity against the target GMIIb enzyme. In contrast, no inhibition effect of the pyrrolidines against LManII was observed. The modification of the imino-L-lyxitol core is therefore a suitable motif for the design of inhibitors with desired selectivity against the target GMIIb enzyme.

Towards inhibitors of glycosyltransferases: A novel approach to the synthesis of 3-acetamido-3-deoxy-D-psicofuranose derivatives.

A novel synthetic strategy leading to 3-acetamido-3-deoxy-D-psicofuranose 9 is presented. The latter compound, after some manipulations, was transformed into fully protected 3-acetamido-3-deoxy-D-psicofuranose 11 as a potential substrate for the synthesis of N-acetylglucosaminyltransferase inhibitors designed by computational methods. After the attempted thioglycosylation of 11 with EtSH in the presence of BF3·OEt2, 2-methyloxazoline derivatives 13 and 14 were isolated.

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

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.

Cyanohydrins from methyl 6-deoxy-2,3-O-isopropylidene-α-l-lyxo-hexofuranosid-4-ulose via Bucherer-Bergs and Strecker reactions.

The formation of methyl 4-cyano-6-deoxy-2,3-O-isopropylidene-α-l-talopyranoside (3), methyl 4-cyano-6-deoxy-2,3-O-isopropylidene-α-l-mannopyranoside (4), methyl 4-cyano-6-deoxy-2,3-O-isopropylidene-ß-d-allopyranoside (5), and methyl 4-cyano-6-deoxy-2,3-O-isopropylidene-ß-d-gulopyranoside (7) from methyl 6-deoxy-2,3-O-isopropylidene-α-l-lyxo-hexopyranosid-4-ulose (1) under Strecker amino nitrile synthesis and Bucherer-Bergs hydantoin synthesis reaction conditions, respectively, is reported. Their structures were determined on the basis of NMR and mass spectral data. The configurations of free cyanohydrins 3 and 4 and 4-O-acetylated cyanohydrins 6 and 8 (obtained by acetylation of 5 and 7, respectively) were established by single-crystal X-ray analysis. The conformations of the six-membered pyranose ring and five-membered 1,3-dioxolane ring in compounds 3, 4, 6, and 8 are also reported.

Synthesis and X-ray structure of a C5-C4-linked glucofuranose-oxazolidin-2-one.

The formation of (4R)-4-carbamoyl-4-[(4R)-3-O-benzyl-1,2-O-isopropylidene-beta-l-threofuranos-4-C-yl]-oxazolidin-2-one instead of expected imidazolidin-2,4-dione (hydantoin) derivative from 5-amino-5-cyano-5-deoxy-3-O-benzyl-1,2-O-isopropylidene-alpha-d-glucofuranose or 3-O-benzyl-1,2-O-isopropylidene-alpha-d-xylo-hexofuranos-5-ulose under Bucherer-Bergs reaction conditions is reported. Single crystal X-ray diffraction data revealed that (3)T(4) is the prefered conformation for the furanose ring, while E(2) and (2)T(1) conformations are adopted by the 1,3-dioxolane and 2-oxazolidinone five-membered rings, respectively.

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

3-(4-Bromophenyl)-5-(4-dimethylaminophenyl)-1-phenyl-2-pyrazoline: X-ray and density functional theory (DFT) studies.

In the crystal structure of the title compound, C(23)H(22)BrN(3), a strong conjugation of the pyrazoline chromophore with the aromatic rings at positions 1 and 3 is observed, as well as a significant shift in the synclinal-->synperiplanar direction. The absolute structure was unequivocally determined. In the absence of clasical hydrogen-bond donors, the structure is stabilized by weak C-H...pi interactions. This paper also reports the electronic structure of the title compound using NBO (natural bond order) analysis. The contributions of lone pairs to the relevant bonds were revealed.

On hydrogen bonding in 1,6-anhydro-beta-D-glucopyranose (levoglucosan): X-ray and neutron diffraction and DFT study.

The geometry of hydrogen bonds in 1,6-anhydro-beta-D-glucopyranose (levoglucosan) is accurately determined by refinement of time-of-flight neutron single-crystal diffraction data. Molecules of levoglucosan are held together by a hydrogen-bond array formed by a combination of strong O-H...O and supporting weaker C-H...O bonds. These are fully and accurately detailed by the neutron diffraction study. The strong hydrogen bonds link molecules in finite chains, with hydroxyl O atoms acting as both donors and acceptors of hydroxyl H atoms. A comparison of molecular and solid-state DFT calculations predicts red shifts of O-H and associated blue shifts of C-H stretching frequencies due to the formation of hydrogen bonds in this system.

2-(4-Hydroxyphenyl)-4,4-dimethyl-2-oxazoline: X-ray and density functional theory study.

In the crystal structure of the title compound, C(11)H(13)NO(2), there are strong intermolecular O-H...N hydrogen bonds which, together with weak intramolecular C-H...O hydrogen bonds, lead to the formation of infinite chains of molecules, held together by weak intermolecular C-H...O hydrogen bonds. A theoretical investigation of the hydrogen bonding, based on density functional theory (DFT) employing periodic boundary conditions, is in agreement with the experimental data. The cluster approach shows that the influence of the crystal field and of hydrogen-bond formation are responsible for the deformation of the 2-oxazoline ring, which is not planar and adopts a (4)T(3) ((C3)T(C2)) conformation.

Synthesis and characterization of new biodegradable hyaluronan alkyl derivatives.

Several new biocompatible and degradable materials were prepared by chemical modification of sodium hyaluronate. The method of activation of hyaluronate by cyanogen bromide was used and subsequent reaction with nucleophile led to the formation of carbamate. This modification of hydroxyl groups of glycosaminoglycans preserves the carboxyl groups and retains properties of polyelectrolyte. This method affords derivatives easily and the reaction condition correlates with degree of substitution. The experimental results show the effect of reaction conditions (reaction time, ratio of reactants) and effect of substitution on biodegradability. The obtained materials were characterized by nuclear magnetic resonance and Fourier transform infrared spectroscopy.

Three isomeric forms of hydroxyphenyl-2-oxazoline: 2-(2-hydroxyphenyl)-2-oxazoline, 2-(3-hydroxyphenyl)-2-oxazoline and 2-(4-hydroxyphenyl)-2-oxazoline.

Crystal structures are reported for three isomeric compounds, namely 2-(2-hydroxyphenyl)-2-oxazoline, (I), 2-(3-hydroxyphenyl)-2-oxazoline, (II), and 2-(4-hydroxyphenyl)-2-oxazoline, (III), all C9H9NO2 [systematic names: 2-(4,5-dihydro-1,3-oxazol-2-yl)phenol, (I), 3-(4,5-dihydro-1,3-oxazol-2-yl)phenol, (II), and 4-(4,5-dihydro-1,3-oxazol-2-yl)phenol, (III)]. In these compounds, the deviation from coplanarity of the oxazoline and benzene rings is dependent on the position of the hydroxy group on the benzene ring. The coplanar arrangement in (I) is stabilized by a strong intramolecular O-H...N hydrogen bond. Surprisingly, the 2-oxazoline ring in molecule B of (II) adopts a 3T4 (C2TC3) conformation, while the 2-oxazoline ring in molecule A, as well as that in (I) and (III), is nearly planar, as expected. Tetramers of molecules of (II) are formed and they are bound together via weak C-H...N hydrogen bonds. In (III), strong intermolecular O-H...N hydrogen bonds and weak intramolecular C-H...O hydrogen bonds lead to the formation of an infinite chain of molecules perpendicular to the b direction. This paper also reports a theoretical investigation of hydrogen bonds, based on density functional theory (DFT) employing periodic boundary conditions.

Synthesis and molecular structure of methyl 4-O-methyl-alpha-D-glucopyranuronate.

A method for the preparation of methyl 4-O-methyl-alpha-D-glucopyranuronate and its single crystal X-ray structure determination are reported. The molecule adopts an almost ideal (4)C1 ((degree)C3) conformation.

Synthesis and structure determination of some nonanomerically C-C-linked serine glycoconjugates structurally related to mannojirimycin.

The Bucherer-Bergs reaction of methyl 2,3-O-isopropylidene-alpha-d-lyxo-hexofuranosid-5-ulose gave (4'S)-4'-carbamoyl-4'-[methyl (4R)-2,3-O-isopropylidene-beta-l-erythrofuranosid-4-C-yl]-oxazolidin-2'-one instead of expected hydantoins. A mixture of hydantoins--(5'R)-triphenylmethoxymethyl-5'-[methyl (4R)-2,3-O-isopropylidene-beta-l-erythrofuranosid-4-C-yl]-imidazolidin-2',4'-dione and (5'S)-triphenylmethoxymethyl-5'-[methyl (4R)-2,3-O-isopropylidene-beta-l-erythrofuranosid-4-C-yl]-imidazolidin-2',4'-dione was obtained from the 5-ulose having protected primary OH group at C-6. The 4'-S configuration of 2 as well as 5'-S configuration of (5'S)-hydroxymethyl-5'-[methyl (4R)-2,3-O-isopropylidene-beta-l-erythrofuranosid-4-C-yl]-imidazolidin-2',4'-dione (9) was confirmed by X-ray crystallography. Corresponding alpha-amino acid--methyl (5S)-5-amino-5-C-carboxy-5-deoxy-alpha-d-lyxo-hexofuranoside (alternative name: 2-[methyl (4R)-beta-l-erythrofuranosid-4-C-yl]-l-serine) (11) was obtained from the hydantoin 9 by acid hydrolysis of the isopropylidene and trityl groups followed by basic hydrolysis of the hydantoin ring. Analogous derivatives with 5-R configuration, formed in a minority, were also isolated and characterised.

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.

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.

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.