{HEAD ~ The free carboxyl moiety} of the adduct is activated with {TAIL ~ a carbodiimide} and a urea group is eliminated by the hydroxylimide catalyst to form an activated ester 
{ HEAD ~ The free carboxyl moiety } of the adduct is activated with { TAIL ~ a carbodiimide } and a urea group is eliminated by the hydroxylimide catalyst to form an activated ester
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH