Combinatorial Enzymatic Synthesis of Unnatural Long-Chain β-Branch Pyrones by a Highly Promiscuous Enzyme

Abstract

In this study, we described in detail a combinatorial enzymatic synthesis approach to produce a series of unnatural long-chain β-branch pyrones. We attempted to investigate the catalytic potential of a highly promiscuous enzyme type III PKS to catalyze the non-decarboxylative condensation reaction by two molecules of fatty acyl diketide-N-acetylcysteines (diketide-NACs) units. Two non-natural long-chain (C16, C18) fatty acyl diketide-NACs were prepared successfully for testing the ability of non-decarboxylative condensation. In vitro, 12 novel naturally unavailable long-chain β-branch pyrones were generated by one-pot formation and characterized by ultraviolet–visible spectroscopy and high-resolution liquid chromatography–mass spectrometry. Interestingly, enzymatic kinetics result displays that this enzyme exhibits the remarkable compatibility to various non-natural long-chain substrates. These results would be useful to deeply understand the catalytic mechanism of this enzyme and further extend the application of enzymatic synthesis of non-natural products.

4-Hydroxy-2-pyrones: Synthesis, Natural Products, and Application

“…PKSs allow for different fragments of carboxylic acids to be involved in the reactions. Also, biological methods were applied for the construction of unnatural 4-hydroxy-2-pyrones using different carboxylic acids as a starter [127][128][129].…”

Current State‐of‐the‐Art Toward Chemoenzymatic Synthesis of Polyketide Natural Products

“…Such a modification enabled visualization and quantification of tagged species with a fluorescent tag, which has been shown to be possible using sulforhodamine B azide [57] or coumarin [58] derivatives (Figure 5A). These strategies have also been applied to the iterative type III csypyrone B1 (CsyB) synthase, wherein a panel of non‐natural aliphatic diketide‐SNAC species was utilized to produce sixteen different pyrones with side chains of differing lengths [59] . Longer chain SNAC analogs have also been utilized for diversification strategies, including a recent study where a hexaketide‐SNAC was used to repurpose the hypothemycin synthase (Hpm3) to produce ( 6’S, 10’S )‐ trans ‐7’,8’‐dehydrozearalenol ( 11 ), as well as other, shorter unnatural resorcylic acid lactones ( 12 – 14 ) (Figure 5B).…”

“…These strategies have also been applied to the iterative type III csypyrone B1 (CsyB) synthase, wherein a panel of non-natural aliphatic diketide-SNAC species was utilized to produce sixteen different pyrones with side chains of differing lengths. [59] Longer chain SNAC analogs have also been utilized for diversification strategies, including a recent study where a hexaketide-SNAC was used to repurpose the hypothemycin synthase (Hpm3) to produce (6'S, 10'S)-trans-7',8'-dehydrozearalenol (11), as well as other, shorter unnatural resorcylic acid lactones (12-14) (Figure 5B). [60] Leveraging synthetic SNAC mimics of natural chain intermediates, numerous research efforts have sought to regioselectively modify existing polyketide scaffolds via non-native chain extensions.…”