Coupling of 3-(3-tert-butyl-4-hydroxyphenyl)propionic acid methylester to I H-benzotriazole using a laccase from Trameteshirsuta was studied. The potentially resulting coupling product Tinuvin 1130 is an important UV-absorber used in polymer based materials. Oxidation of the phenol by the laccase led to homomolecular coupling reactions while the laccase did not attack I H-benzotriazole. Due to the homomolecular reaction of the phenol in the presence of laccase coupling of phenol and IH-benzotriazole was only observed when IH-benzotriazole was applied in four-fold molar excess. The reaction was monitored by UV/vis spectroscopy, TLC and MS (ion trap) analysis. Coupling of IH-benzotriazole took place in ortho position according to the postulated mechanism. (c) 2007 Elsevier Inc. All rights reserved.