1.Chemoselectivity and stereoselectivity of cyclisation pathways leading to bicyclic tetramates controlled by ring-chain tautomerisation in thiazolidines.
Panduwawala TD1, Iqbal S1, Tirfoin R1, Moloney MG1. Org Biomol Chem. 2016 Apr 19. [Epub ahead of print]
Chemoselective Dieckmann cyclisation reactions on N-malonyl thiazolidine templates derived from cysteine and pivaldehyde or aromatic aldehydes may be used to access bicyclic tetramates, for which different pathways operate as a result of differing ring-chain tautomeric behaviour of the respective intermediate imines.
2.Post-translational Claisen Condensation and Decarboxylation en Route to the Bicyclic Core of Pantocin A.
Ghodge SV1, Biernat KA2, Bassett SJ1, Redinbo MR2, Bowers AA1. J Am Chem Soc. 2016 Apr 22. [Epub ahead of print]
Pantocin A (PA) is a member of the growing family of ribosomally encoded and post-translationally modified peptide natural products (RiPPs). PA is much smaller than most known RiPPs, a tripeptide with a tight bicyclic core that appears to be cleaved from the middle of a larger 30-residue precursor peptide. We show here that the enzyme PaaA catalyzes the double dehydration and decarboxylation of two glutamic acid residues in the 30-residue precursor PaaP. Further truncates of PaaP leader and follower peptide sequences demonstrate the different impacts of these two regions on PaaA-mediated tailoring and delineate an essential role for the follower sequence in the decarboxylation step. The crystal structure of apo PaaA is reported, allowing identification of structural features that set PaaA apart from other homologous enzymes that typically do not catalyze such extended post-translational chemistry. Together, these data reveal how additional chemistry can be extracted from a ubiquitous enzyme family toward ribosomally derived peptide natural product biosynthesis and suggest that more examples of such enzymes likely exist in untapped genomic space.