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Hemiacetals and their esters as side-products in lipase-catalysed transesterifications of vinyl esters with sterically hindered alcohols
KTH, Superseded Departments, Chemistry.
KTH, Superseded Departments, Chemistry.
KTH, Superseded Departments, Chemistry.
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2004 (English)In: Journal of Molecular Catalysis B: Enzymatic, ISSN 1381-1177, Vol. 31, 31-37 p.Article in journal (Refereed) Published
Abstract [en]

Lipase-catalysed transesterifications of vinyl esters with various sterically hindered secondary alcohols sometimes give hemiacetals and hemiacetal esters as major side-products along with the expected esters, especially in the presence of aldehydes. The substrates, reaction conditions, and the lipases required for the formation of such hemiacetal products have been studied. Hemiacetals and their esters are very easily hydrolysed. Therefore, when conventional work-up procedures are used, the formation of such products in lipase-catalysed transesterification reactions may easily escape notice, leading to, e.g. an unexpectedly low enantiomeric purity of the isolated remaining substrate in a resolution reaction.

Place, publisher, year, edition, pages
2004. Vol. 31, 31-37 p.
Keyword [en]
lipase, sterically hindered alcohol, hemiacetal esters
National Category
Organic Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-8990DOI: 10.1016/j.molcatb.2004.07.004ISI: 000224575300005OAI: oai:DiVA.org:kth-8990DiVA: diva2:14515
Note
QC 20100831Available from: 2006-01-16 Created: 2006-01-16 Last updated: 2010-12-06Bibliographically approved
In thesis
1. Lipase catalysed reactions of terpenoids : formation of hemiacetal esters : resolution of cryptone and its transformation to cadinenes
Open this publication in new window or tab >>Lipase catalysed reactions of terpenoids : formation of hemiacetal esters : resolution of cryptone and its transformation to cadinenes
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

During attempted enzyme-catalysed resolution of sterically hindered secondary alcohols, hemiacetals and their esters were unexpectedly detected. Hemiacetal esters are reactive compounds that decompose to alcohol, aldehyde and acid under ordinary work-up conditions i.e. in contact with water, acid, or silica gel. Thus, the presence of these side products might decrease the enantiomeric excess of the residual alcohol after workup of a lipase-catalysed resolution. The formation of these hemiacetal esters were further studied using both terpenoid and non-terpenoid substrate alcohols, various acyl donors, and lipases. The prerequisite for their formation is the presence of a sterically hindered substrate alcohol, an aldehyde or an aldehyde releasing acyl donor, and a lipase (PCL-L6, PCL-PS and CAL-B).

Enantioselective synthesis of (S)- and (R)-cryptone was performed via a ring closing metathesis (RCM) of (S)- and (R)-6-isopropyl-1,7-octadien-3-one. The stereochemistry was induced by using pseudoephedrine as chiral auxiliary in an alkylation reaction which provided a chiral octadienone. Problems with removal of the RCM-catalyst resulted in low yields and low enantiomeric purity. In an alternative approach, racemic cryptone was subjected to conjugate addition with thiophenol followed by reduction to the corresponding alcohol. Lipase-catalysed resolution of this alcohol yielded, after oxidation and elimination, (R)- and (S)- cryptone with 76% and 98% ee, respectively.

Marine fouling of immersed objects is a serious problem. Many coatings contain effective antifouling compounds having the drawback of being toxic to the marine environment. The marine natural product 10-isocyano-4-cadinene is a potentially non-toxic antifouling agent against the barnacle Balanus amphitrite and therefore an interesting target for organic synthesis. Cryptone was used as a starting material in attempted syntheses of this compound and other similar model compounds.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 41 p.
Series
Trita-IOK, ISSN 1100-7974 ; 05:99
Keyword
terpenoid, lipase, resolution, hemiacetal, hemiacetal ester, enantioselective, synthesis, cryptone, cadinene
National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-588 (URN)91-7178-225-7 (ISBN)
Public defence
2006-01-27, Sal 0102, Mittuniversitetet, 10:00
Opponent
Note
QC 20100901Available from: 2006-01-16 Created: 2006-01-16 Last updated: 2010-09-01Bibliographically approved

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