Glycine- and sarcosine-based models of vanadate-dependent haloperoxidases in sulfoxygenation reactions.
Reaction of R-styreneoxide with glycine-tert-butylester yielded amino alcohols of the general formula NR1R2R3, where R1 = CH2COOtBu and R2 = R3 = 2-phenyl-2-hydroxyethyl (H2LA); R2 = 2-phenyl-2-hydroxyethyl and R3 = 1-phenyl-2-hydroxyethyl (H2LB); R2 = H and R3 = 2-phenyl-2-hydroxyethyl (HLC); and R2 = H and R3 = 1-phenyl-2-hydroxyethyl (HLD). The corresponding reaction with sarcosine-tert-butylester and subsequent hydrolysis provided the zwitterion +NH(CH3){CH2CHPh(OH)}(CH2CO2-), HLE* (asterisk refers to unprotected carboxylate). Reaction of these ligands with VO(OiPr)3 in CH2Cl2 gave the oxovanadium(V) complexes [VOL(OiPr)2] and [VOL2(OiPr)] (for LC and LD) or, when reacted in the presence of MeOH, [VOL'(OMe)], where L' represents the methyl ester of LA, LB, and LE. The crystal and molecular structures of R-HLC, S-HLD, R,S-HLE* x H2O, and lambda-[VO(R,S-LB')OMe] have been determined. The complex [VOLB'(OMe)] contains vanadium in a distorted trigonal-bipyramidal array (tau = 0.72), the oxo group in the equatorial plane, and methoxide and N in the apical positions, and thus, it structurally models the active center of vanadate-dependent haloperoxidases. The structure and the bonding parameters, including a particularly long d(V-N) of 2.562 A, are backed up by DFT calculations. The isolated oxovanadium(V) complexes and the in situ systems L + VO(OiPr)3 catalyze the oxidation, by cumylhydroperoxide HO2R', of prochiral sulfides (MeSPh, MeSp-Tol, PhSBn) to chiral sulfoxides plus some sulfone. The best results with respect to enantioselectivity (enantiomeric excess (ee) = 38%) were obtained with the system VO(OiPr)3/LA, and the best selectivity with respect to sulfoxide (100%) was obtained with [VOLA(OiPr)]. The reaction with the hexacoordinated [VO(OMe)(HOMe)LD*] was very slow. Oxidation of PhSBn is faster than that of MeSPh and MeSpTol. Turn-over numbers are up to 60 mol of sulfoxide mol-1 of catalyst h-1 (-20 degrees C). The unspectacular ee apparently is a consequence of flexibility of the active catalyst in solution, as shown by the 51V NMR of the catalysts [VOL(OR)] and the oxo-peroxo intermediates [VOL(O2R')]. As shown by DFT calculations, the peroxo ligand coordinates in the tilted end-on fashion in the axial or equatorial position (energy difference = 17.6 kJ/mol).
Wikete
Cornelia
C
Department Chemie, Universität Hamburg, 20146 Hamburg, Germany, Dipartimento di Biotechnologica, Universita di Milano-Bicocca, 20106 Milano, Italy.
Wu
Pingsong
P
Zampella
Giuseppe
G
De Gioia
Luca
L
Licini
Giulia
G
Rehder
Dieter
D
D000465:Algorithms; D002384:Catalysis; D018360:Crystallography, X-Ray; D005998:Glycine / Q000737:chemistry*; D046911:Macromolecular Substances / Q000138:chemical synthesis / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D010544:Peroxidases / Q000737:chemistry*; D012521:Sarcosine / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry*; D014638:Vanadates / Q000737:chemistry*
D046911:Macromolecular Substances; D014638:Vanadates; D013455:Sulfur; D010544:Peroxidases; C026195:bromide peroxidase; D005998:Glycine; D012521:Sarcosine