Intermediates of enalapril maleate

a , n-[1-(s)-(ethoxycarbonyl)-3-phenylpropyl]-l-alanine

(cas no.82717-96-2) ecppa

b , n-[1-(s)-(ethoxycarbonyl)-3-phenylpropyl]-l-alanyl carboxy anhydride

(cas no.84793-24-8) ecppa-nca