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