Reagents suitable for the modification of a bioactive species for the purpose of incorporating one or more phenyldiboronic acid (PDBA) moieties for subsequent conjugation to a different (or the same) bioactive species having one or more pendant boronic compound complexing moieties of the general formula of General Formula I, wherein group R is a reactive electrophilic or nucleophilic moiety suitable for reaction of the PDBA reagent with a bioactive species. Group Z is a spacer selected from a saturated or unsaturated chain up to about 0 to 6 carbon equivalents in length, an unbranched saturated or unsaturated chain of from about 6 to 18 carbon equivalents in length with at least one intermediate amide or disulfide moiety, and a polyethylene glycol chain of from about 3 to 12 carbon equivalents in length. Group Q is a linkage that includes one of amide, ether and thioether moieties. Group R is preferably selected from, but not limited to, one of acrylamide, bromo, bromoacetamide, chloro, chloroacetamide, dithiopyridyl, hydrazide, N-hydroxysuccinimidyl ester, N-hydroxysulfo-succinimidyl ester, imidate ester, imidazolide, iodo, iodoacetamide, maleimide, amino and thiol moieties. Group Z is preferably an unbranched alkyl chain of the general formula (CH2)n, wherein n=1 to 6. Group Q is preferably selected from one of NHCO, CONH, NHCOCH2, CONHCH2, O, OCH2, S, and SCH2 moieties.