| http://www.w3.org/ns/prov#value | - Compounds of particular interest are those of Formula I ##STR1## wherein A is selected from CO and SO2 wherein X is selected from oxygen atom and methylene; wherein each of R1 and R9 is a group independently selected from hydrido, methyl, ethyl, n-propyl, isopropyl, benzyl, ??,??,??-trifluoroethyl, t-butyloxycarbonyl and methoxymethylcarbonyl, and wherein the nitrogen atom to which R1 and R9 are a
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