Knorr Condensation Research Articles

A collagen-associated Ehrlich chromogen: a pyrrolic cross-link?

P r o t e i n a s e d iges t s of c o l l a g e n r i c h t i s sues (bone, tendon, skin, cartilage, periosteum) give a pink colour with dimethylaminobenzaldehyde in acid solution. The chromogen is associated with polymeric collagen, but is a b s e n t f rom n e u t r a l s a l t s o l u b l e co l lagen . It is suggested that amino-ketone forms of collagen crosslinks undergo in vivo a spontaneous Knorr condensation with each other) or with other species, to produce a pyrrolic cross-link.

Lmproved Synthesis of 3-Acetylpyrrole-2-carboxylic Acid

In order to improve the yield of 3-acetylpyrrole-2 carbexylic aeid(APCA) through the Knorr condensation of ethyl acetopyruvate(EAP) with aminoacetaldehyde(AAL), the effects of solvent, reaction temperature and pH were examined. The following conclusions were deduced from these results, (1) The more homogeneous is the reaction system made by the solvent, the higher is the yield of (APCA). (2) The yield of the Knorr condensatien is optimum at 35C and at pH 4.3. (3) The enamine intermediate is formed by the reaction of (EAP) rith aminoacetal(AA)competing with the Knorr condensation. The structure of enamine intermediate is identified by IR spectra and the elementary analysis. (4) (APCA) is obtained by the ring losure of enamine intermediate.

One-step synthesis of 3,5-dihydro-2H-pyrrolo[3,4-d]oxazoles by reaction of p-nitrosophenols with 2-aroylaziridines

Reaction of 1-alkyl-2-aroyl-3-arylaziridines, bearing electron-releasing substituents in the 2- or 3-positions, with substituted p-nitrosophenols give 3,5-dihydro-2H-pyrrolo[3,4-d]oxazoles. The isolation of nitrones and aryl and aroyl imines as secondary products supports the interpretation of the reaction in terms of two consecutive 1,3-dipolar additions, in which the second regiospecific addition is autocatalytic and is followed by a Paal–Knorr condensation.Separate regiospecific addition of ketoaldehydes to 2-aroylaziridines followed by Paal–Knorr condensation with primary amines confirms the proposed reaction scheme and gives excellent yields of 3,5-dihydro-2H-pyrrolo[3,4-d]-oxazoles and related compounds.

Total Synthesis of Pyrrolnitrin. I. Synthesis of 3-Arylpyrrole Derivatives by Knorr's Condensation

Alkyl 3-aryl-5-methyl-4-pyrrolecarboxylate (IIIa-j) and alkyl 2, 5-dimethyl-3-aryl-4-pyrrolecarboxylate (IIIk-m), two kinds of key intermediates for synthesizing pyrrolnitrin (I), were obtained from 2-aminoacetophenones (IV) and alkyl acetoacetate by Knorr's pyrrole synthesis. The mechanism of the pyrrole ringclosure of the above compounds was proposed since alkyl 3-substituted benzoylmethylaminocrotonates (VIII) could be isolated as intermediates presumably because of their difficult cyclization to the corresponding pyrroles ; for which the infrared spectra of nitro and carbonyl group of VIII were discussed.

The chemical synthesis of glucosaminylphosphatidylglycerol. Comparison with a new phospholipid isolated from Bacillus megaterium.

1. We describe the synthesis of a glucosamine derivative of phosphatidylglycerol having the same structure as that of the natural compound isolated from Bacillus megaterium. 2. 2-O-(3,4,6-Tri-O-acetyl-2-deoxy-2-phthalimido-d-glucopyranosyl)-3-O-benzyl-1-iodo-sn-glycerol was prepared by a Königs-Knorr condensation between 3-O-benzyl-1-toluene-p-sulphonyl-sn-glycerol and 3,4,6-tri-O-acetyl-1-bromo-2-deoxy-2-phthalimido-d-glucopyranose followed by replacement of the toluene-p-sulphonyl group with iodine. The iodide was treated with the silver salt of 2-isolauroyl-1-oleoyl-sn-glycerol 3-(monobenzyl hydrogen phosphate) to form the fully protected phosphoglycolipid. 3. Removal of benzyl protecting groups by catalytic hydrogenolysis, phthaloyl group with hydrazine and acetyl groups with pH10 buffer furnished 2-O-(2-amino-2-deoxy-d-glucopyranosyl)-1-(2-isolauroyl-1-stearoyl-sn-glycero-3-phosphoryl)-sn-glycerol. 4. The synthetic and natural compounds appeared identical when compared by chromatography and by identification of hydrolysis products from chemical and enzymic degradations.

CONFIGURATION OF GLYCOSIDIC LINKAGES IN OLIGOSACCHARIDES: IX. SYNTHESIS OF α- AND β-D-MANNOPYRANOSYL DISACCHARIDES

The Königs–Knorr condensation of 4,6-di-O-acetyl-2,3-O-carbonyl-α-D-mannopyranosyl bromide with 1,2,3,4-tetra-O-acetyl-β-D-glucose provides a synthetic route to 6-O-β-D-mannopyranosyl-D-glucose. When some other derivatives of α-D-mannopyranosyl bromide—the 2,3,4,6-tetra-O-benzoyl-, 3,4,6-tri-O-acetyl-, or 3,4,6-tri-O-acetyl-2-O-benzyl derivative—are used as the halide component the α-D-linked isomer of this disaccharide is produced. The steric outcome of Königs–Knorr syntheses involving these and other derivatives of α-D-mannopyranosyl bromide is discussed in terms of the influence of neighboring groups, and of conformational and solvent effects.Lead tetraacetate oxidation of 6-O-β-D-mannopyranosyl-D-glucose, followed by reduction, affords 4-O-β-D-mannopyranosyl-D-erythritol, a metabolite produced by Ustilago species (PRL 627).