the present invention relates to a novel class of phenylboronic acid complexing reagents useful for the preparation of bioconjugates , and the method of making and using such reagents . in the present invention , in the place of prior art avidin - biotin and digoxigenin - anti - digoxigenin systems , phenylboronic acid complexing reagents are utilized in conjunction with phenylboronic acid reagents to facilitate chemical conjugation without the use of intermediary biological macromolecules . reagents suitable for the modification of a bioactive species for the purpose of incorporating a phenylboronic acid complexing moiety for subsequent conjugation to a different bioactive species having pendant phenylboronic acid moieties are of general formula i or general formula ii . ## str1 ## wherein group x is selected from either h , oh , nh 2 , nhch 3 , nhoh and nhoch 3 , wherein group y is selected from either o , s and nh , and wherein group z comprises a spacer which either separates the boronic acid complexing moiety from group r , as in general formula i , or seperates two boronic acid complexing moieties , as in general formula ii . group r is a reactive electrophilic or nucleophilic moiety suitable for reaction of the phenylboronic acid complexing reagent with a bioactive species .