Spontaneous conversions of glutamine, histidine and arginine into alpha-hydroxycarboxylates with NH4VO3 or V2O5

摘要

Glutamine gets transformed to 2-hydroxy-5-oxoproline with NH4VO3 in a neutral solution as a product of 2,2'-bipyridine oxidovanadium(V) 2-hydroxy-5-oxoproline [(V2O3)-O-V(hop)(2)(bpy)(2)]center dot 7H(2)O [1, H(2)hop = 2-hydroxy-5-oxoproline] with yields of 65.6%. Similarly, histidine and arginine are converted into the corresponding alpha-hydroxycarboxylates as 2,2'-bipyridine oxidovanadium(IV) 3-(1H-imidazolyl-5-yl)-2-hydroxyacrylate [(V2O2)-O-IV(imha)(2)(bpy)(2)]center dot bpy [2, H(2)imha = 3-(1H-imidazolyl-5-yl)-2-hydroxyacrylic acid] and guanidinium oxidovanadium(V) 1-(aminoiminomethyl)-2-hydroxyproline (CN3H6)[(VO2)-O-V(Haimhp)(2)]center dot 2H(2)O [3, H(2)aimhp = 1-(aminoiminomethyl)-2-hydroxyproline] with V2O5 in low yields respectively, where an aggregate of oxidovanadium(V) arginine (H(2)arg)(n)((VO3)-O-V)(n)center dot 1/2nH(2)O (4, Harg = arginine) has been isolated preferentially in an initial experiment for 3. alpha-Hydroxycarboxylates chelate bidentately with vanadium via alpha-alkoxy and alpha-carboxy groups in 1-3, as observed from structural analyses. Their racemizations have been observed after the conversions. There is no coordination in 4 based on solid-state C-13 NMR spectra, and only strong hydrogen bonds exist in the anion chains ((VO3)-O-V)(-) and protonated arginines. 1 and 4 were fully characterized by elemental analysis, UV-vis, IR and solid-state C-13 NMR spectroscopies, TG and X-ray structural analyses, and theoretical bond valence calculations (BVS). The conversions of glutamine, histidine and arginine occur spontaneously in a solution under ambient conditions.