Synthesis of cyclic β-turn mimics from l-Pro-Phe/Phe-l-Pro derived di- and tripeptides via ring closing metathesis: the role of chirality of the Phe residue during cyclization

Synthesis of macrocyclic analogues of the neuroprotective agent glycyl-l-prolyl-l-glutamic acid (GPE)

The syntheses of seven macrocyclic analogues of the neuroprotective tripeptide glycyl-L-prolyl-L-glutamic acid (GPE) are described. Macrocycles 6 and 7 mimic the cis conformer of GPE whereas macrocycles 2-5, 8, and 9 mimic the trans conformer of GPE. The macrocyclic peptides of well-defined geometry were prepared via Grubbs ring closing metathesis of an appropriate diene precursor. In turn each of the diene precursors were prepared from the readily available allyl-substituted amino acid building blocks 12, 13, 14, 27, 36 and 51.

A straightforward approach towards cyclic peptides via ring-closing metathesis—scope and limitations

N- and C-terminal diallylated peptides are obtained by several approaches, such as peptide Claisen rearrangement, N- and O- allylation, and the Ugi reaction of allyl-protected components. These diallylated peptides are suitable substrates for ring-closing metathesis and the success of this cyclisation was investigated with respect to the ring size, the position of the allyl moieties and the reaction parameters. In general, excellent yields are obtained for cyclisation of allyl glycine subunits and N-allylated amides, while allyl esters and allyl carbamates often presented serious problems. However, yields of up to 73% were obtained under optimised conditions, and the new generated double bond is formed with excellent trans-selectivity.