Synthesis of the Nonribosomal Peptide Phevalin and Analogs

2(1H)-Pyrazinones from acyclic building blocks: methods of synthesis and further derivatizations

Pyrazinones (2(1H)-pyrazinones) are found as components of a range of natural substances and are involved in the preparation of a great number of bioactive molecules. Synthesis of such compounds, and analogues, requires knowledge of the heterocyclic properties of pyrazinones and, in particular, methods for their ring construction. This review deals with the strategies that have been developed for the synthesis of pyrazinones from acyclic precursors, especially α-amino acid-derived units, from the first examples in 1905 up to the most recent in 2021.

Enzymatic Synthesis of Diverse Heterocycles by a Noncanonical Nonribosomal Peptide Synthetase

Nonribosomal peptide synthetases (NRPSs) are typically multimodular enzymes that assemble amino acids or carboxylic acids into complex natural products. Here, we characterize a monomodular NRPS, PvfC, encoded by the Pseudomonas virulence factor (pvf) gene cluster that is essential for virulence and signaling in different bacterial species. PvfC exhibits a unique adenylation-thiolation-reductase (ATR) domain architecture that is understudied in bacteria. We show that the activity of PvfC is essential in the production of seven leucine-derived heterocyclic natural products, including two pyrazines, a pyrazinone, and a rare disubstituted imidazole, as well as three pyrazine N-oxides that require an additional N-oxygenation step. Mechanistic studies reveal that PvfC, without a canonical peptide-forming domain, makes a dipeptide aldehyde intermediate en route to both the pyrazinone and imidazole. Our work identifies a novel biosynthetic route for the production of pyrazinones, an emerging class of signaling molecules and virulence factors. Our discovery also showcases the ability of monomodular NRPSs to generate amino acid- and dipeptide-aldehydes that lead to diverse natural products. The diversity-prone biosynthesis by the pvf-encoded enzymes sets the stage for further understanding the functions of pvf in bacterial cell-to-cell signaling.

Alkaloids From the Marine Fungus Lecanicillium fusisporum Using an Amino Acid-Directed Strategy

An amino acid-directed strategy has been developed to explore the potential of marine fungi to produce alkaloids. The marine fungus Lecanicillium fusisporum was cultured in glucose-peptone-yeast (GPY) medium to which were added L-tryptophan, L-phenylalanine, L-threonine, D, L-methionine, L-serine, L-lysine and L-valine. A new indole alkaloid, lecasporinoid (1), along with five known alkaloids (2−6) were discovered from the culture broth. The planar structure of lecasporinoid (1) was determined by HR-ESIMS, and 1D and 2D NMR spectroscopic data. The absolute configuration was established by optical rotation and 13C NMR calculations combining with a chemical synthetic approach.