Sitostanol has been converted in high to near-quantitative extent to the corresponding long-chainacyl esters via esterification with oleic acid or transesterification with methyl oleate or trioleoylglycerol using immobilized lipases from
Rhizomucor miehei (Lipozyme IM) and
Candida antarctica(lipase B, Novozym 435) as biocatalysts in vacuo (20-40 mbar) at 80
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C, whereas the conversionwas markedly lower at 60 and 40
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C. Corresponding conversions observed with
papaya (
Caricapapaya) latex lipase were generally lower. High conversion rates observed in transesterification ofsitostanol with methyl oleate at 80
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C using Lipozyme IM were retained even after 10 repeateduses of the biocatalyst. Saturated sterols such as sitostanol and 5
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-cholestan-3
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-ol were the preferredsubstrates as compared to
5-unsaturated cholesterol in transesterification reactions with methyloleate using Lipozyme IM. Transesterification of cholesterol with dimethyl 1,8-octanedioate usingLipozyme IM in vacuo yielded methylcholesteryl 1,8-octanedioate (75%) and dicholesteryl 1,8-octanedioate (5%). However, transesterification of cholesterol with diethyl carbonate and that ofoleyl alcohol with ethylcholesteryl carbonate, both catalyzed by Lipozyme IM, gave ethylcholesterylcarbonate and oleylcholesteryl carbonate, respectively, in low yield (20%). Moreover, cholesterolwas transesterified with ethyl dihydrocinnamate using Lipozyme IM to give cholesteryl dihydrocinnamate in moderate yield (56%), whereas the corresponding reaction of lanosterol gave lanosteryloleate in low yield (14%).Keywords: Candida antarctica lipase B; Carica
papaya lipase; esterification and transesterificationin vacuo; fatty acids; Rhizomucor miehei lipase; solvent-free esterification and transesterification;stanyl esters; steryl esters