Abstract
The importance of biologically active cyclic phosphorus systems has become increasingly apparent relatively recently; particularly, for example, with the discoveries of the cellular “second messenger” activities of cyclic 3′, 5′-adenosine and guanosine monophosphates and the powerful cancer therapeutic capabilities of cyclo-phosphamide and its cyclic metabolites. The earlier recognition that cyclic 2′, 3′-nucleotides formed as intermediates in the hydrolysis of polynucleotides, led to the classic researches of Westheimer and his coworkers on the hydrolysis rates of cyclic and acyclic phosphate esters.1 Within the few years the extreme toxicities of bicyclic phosphorus esters compared to their acyclic analogues have come to light2,3 along with the surprising observation that the cholinesterase inhibition of such cages is only negligible.3,4