g 1 42 mmol of butanoic acid 3 mercapto 3 methyl 2 e 1 4 4 hydroxy 4 oxobutoxy phenyl ethylidene hydrazide example 1 or 2 and 0 22 g 1 89 mmol of n hydroxysuccinimide is added 10 ml of n n dimethylformamide followed by the rapid addition of 0 70 g 3 65 mmol of 1 3 dimethylaminopropyl 3 ethylcarbodiimide hydrochloride and the mixture stirred at room temperature for 3 hours the reaction mixture is concentrated in vacuo to a residue which is partitioned between ethyl acetate and water the separated organic layer is washed with water saturated sodium chloride and dried mgso 4 the organic layer is evaporated in vacuo to give an oily residue which crystallized from ethyl acetate hexane affording 0 21 g of the title compound as a colorless solid a mixture of butanoic acid 3 mercapto 3 methyl 2 e 1 4 4 hydroxy 4 oxobutoxy phenyl ethylidene hydrazide examples 1 or 2 3 69 g 10 48 mmol and n hydroxysuccinimide 1 386 g 12 05 mmol is suspended in dioxane 60 ml dcc 2 482 g 12 05 mmol in dioxane 30 ml is added dropwise over 15 min the mixture is stirred at room temperature for 24 h the.