title: Reactions of D-glucose with phenolic amino acids: further insights into the competition between Maillard and Pictet-Spengler condensation pathways.
abstract: The reactions of 5-S-cysteinyldopa, L-alpha-methyldopa and DL-m-tyrosine with D-glucose were investigated at 90 degrees C in phosphate buffer at pH ranging from 5.0 to 9.0. Whereas gave mainly the double Maillard condensation product N,N'-bis(1''-deoxy-D-fructos-1''-yl)-5-S-cysteinyldopa, as an inseparable mixture of beta-D-fructopyranosyl and alpha,beta-D-fructofuranosyl derivatives, 2 and 3 gave both Maillard and Pictet-Spengler products, although to different extents and with different regio- and stereochemistry. A peculiar pattern of reactivity was displayed by which gave, besides the Maillard product and the expected 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline C-1 diastereoisomeric pairs, the unprecedented 7,8-dihydroxy-1,2,3,4-tetrahydroisoquinoline derivative via the ortho cyclization pathway. Pictet-Spengler cyclization of 2 and 3 proceeded with Felkin-Anh-type asymmetric induction, favouring the 1R isomer throughout the pH range 5.0-9.0. These results, which highlight the first example of carbohydrate-derived 7,8-dihydroxytetrahydroisoquinoline, provide new insights into the factors governing competition between Maillard and Pictet-Spengler condensation pathways.
authors.affiliation: Department of Organic Chemistry and Biochemistry, University of Naples Federico II, Complesso Universitario Monte Sant'Angelo, Via Cinthia 4, I-80126 Naples, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Manini
authors.forename: Alessandra
authors.initials: A
authors.lastname: Napolitano
authors.forename: Marco
authors.initials: M
authors.lastname: d'Ischia
mesh_terms: D002384:Catalysis; D003548:Cysteinyldopa / Q000737:chemistry*; D005947:Glucose / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D015416:Maillard Reaction; D019216:Metals, Heavy / Q000737:chemistry; D008750:Methyldopa / Q000737:chemistry*; D008968:Molecular Conformation; D013237:Stereoisomerism; D014443:Tyrosine / Q000737:chemistry*
chemical_list: D019216:Metals, Heavy; D003548:Cysteinyldopa; D014443:Tyrosine; D008750:Methyldopa; C015566:3-tyrosine; D005947:Glucose