ORIGINAL ARTICLE Lipase-catalyzed regioselective protection/deprotection of hydroxyl groups of the isoflavone irilone isolated from Iris germanica NIGHAT NAZIR 1 , SURRINDER KOUL 2 , MUSHTAQ AHMAD QURISHI 1 , SUBHASH CHANDRA TANEJA 2 , & GHULAM NABI QAZI 2 1 Department of Chemistry, University of Kashmir, Hazratbal, Srinagar-190006, J&K, India and 2 Biotechnology Division, Indian Institute of Integrative Medicine, Canal Road, Jammu-180001, J&K, India Abstract The regioselective acylation of irilone, isolated from Iris germanica, with vinylacetate and propenylacetate and deacylation of irilone diacetate with n-butanol were studied using lipases from Aspergillus niger, Mucor miehei, Pseudomonas cepacia, Candida cylindracea, porcine pancreas and Candida antarctica. Significant conversion of irilone to 4?-O-acetylirilone was achieved using P. cepacia lipase, while irilone diacetate was converted to 5-O-acetylirilone by the enzymatic action of lipases from M. miechei, P. cepacia and porcine pancreas under different experimental conditions. This preferential protection/deprotection furnishes an opportunity to modify the structure of irilone by selective derivatization that may help to change its biological activities by modifying its amphiphilic/lipophilic balance. Keywords: Lipase, irilone, acetylation, regioselectivity, Iris germanica Introduction Polyphenolic compounds produced by plants are of considerable research interest, both as functional food ingredients and as nutraceuticals. Flavonoids are among the most ubiquitous groups of polyphe- nolic compounds in foods of plant origin. As integral constituents of the diet, they may exert a wide range of beneficial effects on human health. Biological activities of flavonoids exploitable in the biomedical field include anti-inflammatory (Guardia et al. 2001, Na et al. 2003), antiviral (Li et al. 2000), anticancer (Birt et al. 2001), anticoagulant (Gaalnur et al. 2004), antiatherosclerosis, low-density lipoprotein (LDL) oxidation inhibitory (Aviram & Fuhrman 1998), antioxidant (Heim et al. 2002), immunomo- dulatory (Liang et al. 1997) and antitumor (Yasu- kawa et al. 1990) activities. In addition, they are also known as potential cell growth inhibitors (Casagrande & Darbon 2001) and multidrug resis- tance modulators (Leslie et al. 2001). By virtue of their capacity to inhibit LDL oxidation, flavonoids have demonstrated a unique cardioprotective effect (Mazur et al. 1999). Because of these biological properties, flavonoids are of considerable research interest and are used in food, cosmetics and pharmaceutical preparations (Harborne & Williams 2000). Unfortunately, a large number of flavonoids show low solubility in lipo- philic media with a consequent low bioavailability (Manach et al. 2005), limiting their efficacious use. In order to improve these properties, several authors have studied the modification of their structures by chemical, enzymatic and chemoenzymatic methods. Two reactions, i.e. glycosylation and acetylation, have received special interest as these are known to modify the hydrophilic/lipophilic balance of flavo- noids. The former modification reinforces their hydrophilicity by addition of a sugar moiety while the latter makes them more hydrophobic by the addition of acyl groups, thereby improving their bioavailability (Viljanen et al. 2005). Being non- regioselective, the chemical acylation of flavonoids leads to an unwanted derivatization of all hydroxyl groups, including the active ones, resulting in either reduction or complete loss of biological activity of the molecules (Chen et al. 1999). Therefore, selec- tive protection/deprotection of specific hydroxyl Correspondence: Nighat Nazir, Department of Chemistry, University of Kashmir, Hazratbal, Srinagar-190006, J&K, India. Tel: 91-194- 2424900. Fax: 91-194-2421357. E-mail: nighat052000@yahoo.com.au Biocatalysis and Biotransformation, MarchApril 2009; 27(2): 118123 ISSN 1024-2422 print/ISSN 1029-2446 online # 2009 Informa UK Ltd DOI: 10.1080/10242420802583457