<p> </p><p>A chemoselective catalyst is preferred in a chemical reaction where protecting groups otherwise are needed. The two lipases <em>Candida antarctica </em>lipase B and <em>Rhizomucor miehei</em> lipase showed large chemoselectivity ratios, defined as (<em>k<sub>cat</sub></em>/<em>K</em><sub>M</sub>)<sub>OH </sub>/ (<em>k<sub>cat</sub></em>/<em>K</em><sub>M</sub>)<sub>SH</sub>, in a transacylation reaction with ethyl octanoate as acyl donor and hexanol or hexanethiol as acyl acceptor (<strong>paper I</strong>). The chemoselectivity ratio of the uncatalyzed reaction was 120 in favour of the alcohol. Compared to the uncatalyzed reaction, the chemoselectivity was 730 times higher for <em>Candida antarctica </em>lipase B and ten times higher for <em>Rhizomucor miehei</em> lipase. The <em>K</em><sub>M</sub> towards the thiol was more than two orders of magnitude higher than the <em>K</em><sub>M</sub> towards the corresponding alcohol. This was the dominating contribution to the high chemoselectivity displayed by the two lipases. In a novel approach, <em>Candida antarctica </em>lipase B was used as catalyst for enzymatic synthesis of thiol-functionalized polyesters in a one-pot reaction without using protecting groups (<strong>paper II</strong>). Poly(e-caprolactone) with a free thiol at one of the ends was synthesized in an enzymatic ring-opening polymerization initiated with mercaptoethanol or terminated with either 3-mercaptopropionic acid or g-thiobutyrolactone.</p><p> </p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:kth-10232 |
| Date | January 2009 |
| Creators | Hedfors, Cecilia |
| Publisher | KTH, School of Biotechnology (BIO), Stockholm : UniversitetsService US AB |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Licentiate thesis, comprehensive summary, text |
| Relation | Trita-BIO-Report, 1654-2312 ; 2009:7 |
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