Equilibrium kinetics of the new experimental anti-tumour compound SK&F 104864-A in aqueous solution

The equilibrium kinetics of lactone ring hydrolysis in the new experimental anti-tumour compound SK&F 104864-A. (S)-dimethylaminomethyl-10-hydroxycamptothecin hydrochloride, have been studied. Only one product is formed, SK&F 105992. A stability-indicating HPLC method has been optimized to perform the analysis. The pH is the main factor influencing equilibrium; at pH greater than or equal to 10 the lactone ring is quantitatively opened while at pH values less than or equal to 4 the lactone form is exclusively present. Other parameters, such as buffer ions and ionic strength, do not influence equilibrium. Complexation with dimethyl-beta-cyclodextrin stabilizes the lactone form. Other cyclodextrins do not show this stabilization.