Degradation kinetics of three gonadorelin analogues: developing a method for calculating epimerization parameters.
OBJECTIVE
To develop a method for calculating epimerisation parameters, find out if the kinetics of the independent reactions can be established, and elucidate primary structure-chemical degradation relationships in the degradation kinetics of three gonadorelin analogues.


METHODS
The influences of pH, temperature, and buffer concentration on the degradation of the three gonadorelin analogues buserelin, goserelin, and triptorelin were investigated using RP-HPLC. A method was developed to calculate epimerisation and hydrolysis rate constants independently.


RESULTS
Explicit structure-degradation mechanism relations were found in the degradation of all three compounds. The L-serine residue was found to be involved in both a solvent-catalysed backbone hydrolysis and a hydroxyl-catalysed epimerisation whereas, the O-tertiary butyl D-serine residue was only involved in proton-catalysed ether hydrolysis. The kinetics of identical reactions in different analogues were generally comparable.


CONCLUSIONS
The degradation of the gonadorelin analogues is located at a relatively small number of chemical residues and prediction of the degradation mechanisms and kinetics of other peptides with similar structural elements appears to be possible.
Department of Pharmaceutical Analysis, Faculty of Pharmacy, Utrecht University, The Netherlands. m.a.hoitink@far.ruu.nl
M A
MA
Hoitink
J H
JH
Beijnen
M U
MU
Boschma
A
A
Bult
O A
OA
van der Houwen
G
G
Wiese
W J
WJ
Underberg
D002021:Buffers; D002064:Buserelin / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives*; D017273:Goserelin / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008956:Models, Chemical; D011487:Protein Conformation; D013696:Temperature; D017329:Triptorelin Pamoate / Q000737:chemistry*
D002021:Buffers; D017329:Triptorelin Pamoate; D017273:Goserelin; D007987:Gonadotropin-Releasing Hormone; D002064:Buserelin