Boron compound completing reagents, intermediate reagents of those reagents and methods of synthesizing these reagents. These reagents, including those shown as General Formula CII may be used, after further reactions described herein, to complex with boronic compounds, such as phenylboronic acid or derivatives thereof. ##STR1## In one embodiment, group Z comprises 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 of intermediate amide and disulfide moieties, and a polyethylene glycol chain of from 3 to 12 carbon equivalents in length; group R.sub.2 is one of an alkyl and a methylene with an electronegative moiety; and BAS is a biologically active species.