The estrification of L-trans-epoxysuccinic acid hemi-ethyl ester (I) with 4-nitrophenol (II) by means of dicyclohexylcarbodiimide (DCC) gives the corresponding p-nitrophenyl ester (III), which is then condensed with N-isoamyl L-leucinamide (IV).

The estrification of L-trans-epoxysuccinic acid hemi-ethyl ester (I) with 4-nitrophenol (II) by means of dicyclohexylcarbodiimide (DCC) gives the corresponding p-nitrophenyl ester (III), which is then condensed with N-isoamyl L-leucinamide (IV).

The synthesis of [14 C]-EST has been described ac cording to the following procedure: The oxidation of fumaric acid (I) with H2O2 gives trans-epoxysuccinic acid (II), which is submitted to optical resolution by means of its salt with L-arginine. The L-trans isomer (III) is esterified with ethanol and H2SO4 to the corresponding diethyl ester (IV), which is hydrolyzed selectively with KOH, affording the monoethyl ester (V). Finally, this monoester 5 condensed with N-isoamyl-L-leucinamide (VI).

The synthesis of [14 C]-EST has been described ac cording to the following procedure: The oxidation of fumaric acid (I) with H2O2 gives trans-epoxysuccinic acid (II), which is submitted to optical resolution by means of its salt with L-arginine. The L-trans isomer (III) is esterified with ethanol and H2SO4 to the corresponding diethyl ester (IV), which is hydrolyzed selectively with KOH, affording the monoethyl ester (V). Finally, this monoester 5 condensed with N-isoamyl-L-leucinamide (VI).