Synthesis of Ferrocenoyl Peptides

The acid chloride method was successfully employed to produce a number of l,T-disubstituted ferrocenoyl peptide and amino acid systems, such as Herrick s l,r-ferrocenoyl-prolinyhnethylester (5) and Hirao s l,T-ferrocenoyl- )w-alanyl-prolinylesters (6).  

Interestingly, using the HOBt, l-oligoprolmoyl-l -OBt-ferrocene derivatives (12-14) were obtained as byproducts. This class of compounds is a convenient starting material en route to asymmetrically substituted ferrocenoyl derivatives, such as compound 18. 

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Scheme 5 Synthesis of ferrocenoyl peptides (4) via the ferrocenyl oxazolone (20) starting from a ferrocenoyl amino acid (19) (a) DCC or EDC, (b) amino acid.

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