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Peptide esters coordinated in a chelate fashion as in 1 (M = Rh, R = Me) may be extended on the amino ends by reaction with α-amino acid esters in the presence of base. In the case of L-leucine methyl ester the resulting tripeptide ester can be cleaved from the metal center with virtually no racemization. The organometallic reagent [{(C5Me5)RhCl2}2] can be recovered.
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Beck et al. (1991) studied this question.
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