Cyclopeptides have wide-ranging applications in the fields of biomedicine and nanotechnology.1 They display cross membrane properties, resistance to in vivo enzymatic degradation and are able to effectively modulate protein protein interactions.2
Patellamides represent an interesting class of natural cyclic peptides, and it has been shown that they exhibit anticancer properties in vitro.3 Recently, the Naismith group reported the in vitro biosynthesis of patellamide-like cyclopeptides by employing the natural enzymes of patellamide pathway.4
Total synthesis approaches to patellamides have been reported but require at least 14 steps.5 The inability to generate highly chemically diverse patellamide analogs on a useful scale has hindered their development as potential drug lead molecules.
In this communication6, we propose a new approach to patellamides which combines the advantages of solid-phase synthesis to prepare a library of highly diverse substrates with in vitro enzymatic reactions employing a pool of enzymes of the patellamide class, that introduce modifications difficult to achieve by simple chemical means. A resin-bound peptide containing a base cleavable linker is cleaved to release the deprotected linear peptide in solution, and consequently through the sequential addition of several enzymes in "one-pot" strategy we can introduce heterocycles, selectively oxidise thiazolines or oxidise both thiazolines and oxazolines, and finally macrocyclise the substrate. Non natural amino acids can also be introduced. This new method has been successfully employed to produce patellamide analogs on mg scale.
The in house chemoenzymatic production of patellamide C, D employing the new route disclosed that an epimer of authentic patellamide C, D is obtained. A 1H NMR doping experiment with authentic patellamide has been carried out.
The stereochemical assignment of epi epi patellamide C, D has been achieved by chemical synthesis of model compounds and DFT calculations. Epimerization of patellamides was discovered to be not chemically spontaneous.