Heterocyclen aus Zuckern [1] Chinoxaline und 1H‐Pyrazolo[3.4‐b]chinoxaline („Flavazole”︁)

Reducing disaccharides and their 1,2-dicarbonyl intermediates as building blocks for nitrogen heterocycles

“…Based on the disaccharide starting material, products were obtained that are distinguished by diverse glycosylation patterns on the tetrahydroxybutyl side chain (see Scheme 3 and Table 1). The developed synthesis procedures can be easily transferred into large scale production and the produced N-heterocycles of the quinoxaline- (3,8,(13)(14)(15)(16)(17)(18), pyrazolo [3,4b] quinoxaline- (10), triazine-( 9) and pyrazine-(11 and 12) type can provide suitable raw materials for novel high value products with unique properties based on their carbohydrate origin.…”

“…The key 1,2-dicarbony building block 1 (2-keto-Dglucose) 33,34,42,43 enables access to N-heterocycles of the pyrazolo [3,4b]quinoxaline-(2), 16,21,22 quinoxaline-(3) 16,17 and 1,2,4-triazinetype (4). 35 Scheme 2 Reactive 1,2-dicarbonyl intermediate synthesis (method A and B employing phenyl osazone intermediate 5 / 7.…”

“…10,12,13 Other work has expanded on the utilization of sugar phenylosazones as building blocks for the synthesis of prrazoles. [13][14][15] Rare examples of direct single step conversions of natural reducing sugars into aromatic N-heterocycles, lead to quinoxalines, 16,17 pyrazines, 18 imidazoles, [19][20][21] fused ring pyrazolo [3,4-b]quinoxalines 16,22,23 and benzimidazoles. [24][25][26] Here we exploit reducing carbohydrates as a source of 1,2dicarbonyl-building blocks (diuloses) and their conversion into N-heterocycles.…”

“…33,34 These biotechnological produced dicarbonyl sugars show potential as building blocks for heterocycle synthesis. [35][36][37][38] In particular, the 1,2-dicarbonyl sugar, D-glucoson 1 was used to access heterocycles (Scheme 1) of the quinoxaline type 16,17 / 3 the pyrazolo [3,4-b]quinoxaline type 16,22,23 / 2 and 1,2,4 triazine / 4 type. 35 The selective bioconversion of disaccharides into the related 1,2-dicarbonyl analogues is only limited realized for the (1 / 6) linked disaccharides gentiobiose, isomaltose, melibiose and the (1 / 4) linked lactose.…”

Conversion of reducing carbohydrates into hydrophilic substituted imidazoles

“…10,12,13 Furthermore, Lichtenthaler and coworkers [13][14][15] expanded on the utilization of sugar phenyl osazones as building blocks for the synthesis of pyrrazoles. [13][14][15] Other rare examples of direct single step conversions of natural reducing sugars into aromatic N-heterocycles has lead to quinoxalines, 16,17 pyrazines, 18 imidazoles, 19,20 fused ring pyrazolo [3,4-b]quinoxalines 16,21,22 and benzimidazoles. [23][24][25] In this work we were particularly interested in the synthesis of imidazoles.…”