Disclosed is a phenyl boronic acid compound represented by Structural Formula (I): ##STR00001## Ar is a substituted or unsubstituted aryl group. Z and Z' are independently --O--, --NH-- or --S--. X is an electron withdrawing group. R is a substituted or unsubstituted straight chained hydrocarbyl group optionally comprising one or more amine, ammonium, ether, thioether or phenylene linking groups and Y is --H, an amine, --[NH--(CH.sub.2).sub.q].sub.r--NH.sub.2, halogen, --CF.sub.3, thiol, ammonium, alcohol, --COOH, --SO.sub.3H, --OSO.sub.3H or phosphonium group covalently bonded to the terminal position of R. Each --NH-- in --[NH--(CH.sub.2).sub.q].sub.r--NH.sub.2 is optionally N-alkylated or N,N-dialkylated and --NH.sub.2 in --[NH--CH.sub.2).sub.q].sub.r--NH.sub.2 is optionally N-alkylated, N,N-dialkylated or N,N,N-trialkylated. q is an integer from 2 to about 10 and r is an integer from 1 to about 5. R.sub.1 and R.sub.1' are independently --H, an aliphatic group, a substituted aliphatic group, an aryl group or a substituted aryl group, or, taken together, are a C2-C5 substituted or unsubstituted alkylene group optionally comprising an amine linking group [--N.sup.+(R.sup.1a)--]. Each R.sub.1 is Structural Formula (I) is preferably --H. R.sup.1a is --H, alkyl, substituted alkyl phenyl or substituted phenyl. Also disclosed is a method of treating obesity in a subject by administering an effective amount of a compound represented by Structural Formula (I) and a pharmaceutical composition comprising the compound and a pharmaceutically acceptable carrier or diluent.