Few bicyclic acetals at reducing end of low-molecular-weight heparins: might they restrict specification of pharmacopoeia?

ABSTRACT

The alkaline hydrolysis of heparin benzyl ester originates enoxaparin. The depolymerization by beta-elimination is the primary effect of reaction; but side reactions can happen and the bicyclic acetal at the reducing end of glucosamine N,6-disulphate, called 1,6-anhydro ring, is a product of a side reaction. The amount of this predictable moiety of enoxaparin can be controlled to a lowest extent (6%) and to extent higher than 40% by modulating the alkalinity and duration of the reaction of hydrolysis. With the exclusion of the beta-elimination effects and of these non significative side reactions, the chemical structure of the parent heparin is entirely maintained in enoxaparin as it results by the same profiles of constituent disaccharides. The content of 1,6-anhydro rings is assessed by a not yet validated NMR method. The chains of enoxaparin bearing, at their reducing end, 1,6-anhydro rings could be regarded as Related Substances of enoxaparin. If present, even in an amount less than, or equal to, 30% of chains, these "related substances" affect neither activities nor safety of enoxaparin.