| http://www.w3.org/ns/prov#value | - R.sub.2, X', Y', U, Alk.sub.1 and Alk.sub.2 have the above definitions and when X' and/or Y' are other than hydrogen, reacting the latter an agent to protect the amino group to form a compound of the formula ##STR16## wherein R.sub.2, Alk.sub.1,
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