Structure of aldose condensation products with 2-hydroxyand 2-sulfanylbenzohydrazides

Abstract

The structure of the condensation products of 2-hydroxy-and 2-sulfanylbenzohydrazides with a series of aldoses (L-arabinose, D-ribose, L-ramnose, D-galactose, D-glucose, D-mannose) was studied by 1 H and 13 C NMR spectroscopy. The condensation products of monosaccharides with 2-hydroxybenzohydrazide in DMSO-d 6 solution exist as equilibrium mixtures of linear hydrazone and cyclic pyranose and furanose forms, the cyclic tautomers being represented by two stereoisomers (α-and β-anomers). The aldose condensation products with 2-sulfanylbenzohydrazide in the crystalline state have cyclic 1,3,4-benzothiadiazepine structure, while in DMSO-d 6 solution they undergo complete or partial isomerization into cyclic pyranose tautomer.Condensation products of 2-sulfanylbenzohydrazide with monocarbonyl compounds tend to undergo intramolecular cyclization via nucleophilic addition of the SH group at the C=N bond with formation of seven-membered benzo-1,3,4-thiadiazepine ring [1-3]. In some cases this process is reversible, so that equilibrium mixture of linear 2-sulfanylbenzoylhydrazone and cyclic benzothiadiazepine tautomers may exist in solution.In continuation of our previous studies [1-3], in the present work we examined the structure of the condensation products obtained from 2-hydroxy-and 2-sulfanylbenzohydrazides IIa and IIb and a series of aldoses Ia-If. Compounds IIIa-IIIl were synthesized in good yields (55-90%) by heating equimolar amounts of the corresponding monosaccharide (L-arabinose, D-ribose, L-ramnose, D-galactose, D-glucose, D-mannose) and hydrazide in boiling methanol for a short time (see Experimental).2-Hydroxy-and 2-sylfanylbenzoylhydrazones IIIaIIIl are complex tautomeric systems that are capable of existing as cyclic five-and six-membered tautomers A and C and linear hydrazone structure B. In addition, condensation products IIIg-IIIl derived from aldoses and 2-sulfanylbenzohydrazide (IIb) could give rise to seven-membered 1,3,4-benzothiadiazepine form D as a result of attack by the SH group on the C=N bond. It should be also taken into account that each cyclic form A, C, and D may be a mixture of two stereoisomers [α-and β-anomers for structures A and C and (2R)-and (2S)-stereoisomers for structure D]. The formation of analogous seven-membered cyclic 1,3,4-benzoxadiazepine tautomers for 2-hydroxybenzoylhydrazones IIIa-IIIf via attack by the OH group on the C=N bond should be ruled out. It is known that condensation products of 2-hydroxybenzohydrazide with aldehydes and ketones have exclusively linear structure and they do not tend to undergo the above cyclization [4,5].In all experiments, the 1 H and 13 C NMR spectra were recorded at definite time intervals starting from the moment of dissolution until the end of transformations. In addition, the structure of the compounds under study in the crystalline state was confirmed by solid-phase high-resolution 13 C NMR spectroscopy

Structure of Aldoses Condensation Products with 2-Hydroxy- and 2-Aminobenzohydrazides

“…In addition, the structure of the compounds under study in the crystalline state was confirmed by solid-phase high-resolution 13 C-NMR spectroscopy (CPMAS). For example, pyranose form B was expected to give a signal from the anomeric C-1 atom at δ 85 -90 ppm; analogous signal from five-membered furanose tautomer C is located at δ 95 -100 ppm [6] [7]. The C-1 signal of possible benzo-1,2,4-triazepin tautomer D should appear in a stronger field, at δ 70-75 ppm, which is typical of sp 3 -hybridized carbon atom in seven-membered ring, located between two nitrogen atoms [4] [5].…”

Structure of Aldoses Condensation Products with SH-Containing Hydrazides

“…To a solution of 0.01 mol of SH-containing hydrazide in 25 ml of methanol 0.01 mol of an appropriate aldose was added, and the mixture was boiled for a period of 1-3 h. The solvent was removed at a reduced pressure, and the residue was washed with ether (3 × 50 ml), and the colorless crystalline substance was filtered off on a glass filter funnel (40 -100 μm), dried and stored in a desiccator over P Spectral characteristics of compounds 1b-1e, 2b-2f, 3b-2f, and 4b-4f were described previously [9]- [12].…”