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