ANTICANCER AGENTS .15. SQUARIC ACID DIETHYL ESTER - A NEW COUPLING REAGENT FOR THE FORMATION OF DRUG BIOPOLYMER CONJUGATES - SYNTHESIS OF SQUARIC ACID ESTER AMIDES AND DIAMIDES

Reaction of squaric acid diethyl ester (1) with a slight excess of a primary or secondary amine 2 in ethanol, dichloromethane or aqueous buffer (pH 7) at 20-degrees-C for 0.3-12 h gives the squaric acid amide esters 3 in mostly excellent yields. Treatment of 3 with amines 2 or 4 in organic solvents in the presence of triethylamine or in aqueous buffer (pH 9) leads to the corresponding symmetrical and unsymmetrical squaric acid diamides 5, respectively. The reaction can be followed by UV spectroscopy.