Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
5
pubmed:dateCreated
1992-7-22
pubmed:abstractText
The kinetics of isomerization of cyclosporin A to isocyclosporin A were studied in various nonaqueous solvents as a function of temperature and added methanesulfonic acid. The rate of isomerization was found to be acid-catalyzed over the acid concentration range studied. The choice of organic solvent significantly altered the rate of isomerization. For a series of alcohols, the rate was enhanced with increasing dielectric constant of the media, however, this correlation did not hold upon introduction of the dipolar aprotic solvent, tetrahydrofuran. Conversion of cyclosporin A to isocyclosporin A in tetrahydrofuran was found to contain diminished side reactions as compared to alcoholic solvents. The rate of conversion of isocyclosporin A to cyclosporin A was determined in aqueous buffers as a function of pH, buffer concentration, and temperature. The rates of conversion were extremely rapid compared to the forward reaction. Based on the pH dependencies of dilute solution reactivities, isocyclosporin A displayed a kinetically generated pKa value of 6.9 for the secondary amine moiety. From pH 8 to pH 10 the pH-rate profile plot is linear, with a slope approximately equal to unity, indicating apparent hydroxide ion catalysis. The break in pH-rate profile suggests a change in the rate-determining step upon protonation of isocyclosporin A. The rate of isomerization in plasma was comparable with that found in a pH 7.4 buffer solution, indicating that plasma proteins do not significantly alter the isomerization kinetics of isocyclosporin A to cyclosporin A.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
May
pubmed:issn
0724-8741
pubmed:author
pubmed:issnType
Print
pubmed:volume
9
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
617-22
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
1992
pubmed:articleTitle
Kinetics and mechanism of isomerization of cyclosporin A.
pubmed:affiliation
Department of Pharmaceutical Chemistry, University of Kansas, Lawrence 66045.
pubmed:publicationType
Journal Article, Comparative Study, Research Support, U.S. Gov't, P.H.S., Research Support, Non-U.S. Gov't