An enzymatic [4+2] cyclization cascade creates the pentacyclic core of pyrroindomycins

Abstract

The [4+2] cycloaddition remains one of the most intriguing transformations in synthetic and natural products chemistry. In nature, however, there are remarkably few enzymes known to have this activity. We herein report an unprecedented enzymatic [4+2] cyclization cascade that has a central role in the biosynthesis of pyrroindomycins, which are pentacyclic spirotetramate natural products. Beginning with a linear intermediate that contains two pairs of 1,3-diene and alkene groups, the dedicated cyclases PyrE3 and PyrI4 act in tandem to catalyze the formation of two cyclohexene rings in the dialkyldecalin system and the tetramate spiro-conjugate of the molecules. The two cyclizations are completely enzyme dependent and proceed in a regio- and stereoselective manner to establish the enantiomerically pure pentacyclic core. Analysis of a related spirotetronate pathway confirms that homologs are functionally exchangeable, establishing the generality of these findings and explaining how nature creates diverse active molecules with similar rigid scaffolds.

Metabolic Engineering of Microorganisms for the Production of Natural Compounds

“…Especially, investigation of traditional oriental medicines will propose many more novel natural product targets for microbial production. [290] Moreover, with novel enzymes being uncovered, such as the ones in charge of 4+2 cyclic reaction [291] and alkyne biosynthesis, [292] discovery and production of novel natural compounds by metabolic engineering has been greatly facilitated. Overall, cumulated systems biological techniques with recently being developed innovative engineering tools would greatly accelerate this field of research with the objective of providing invaluable natural compounds efficiently.…”

Characterization of the biosynthetic gene cluster for maklamicin, a spirotetronate-class antibiotic of the endophytic Micromonospora sp. NBRC 110955

“…Genes encoding a transcriptional regulator of the TetR family and an MFS transporter are well-conserved among the gene clusters of maklamicin, chlorothricin, kijanimicin, and tetrocarcin A, suggesting that these two genes, in addition to the biosynthetic genes for the polyketide backbone and the tetronate moiety, play a common role in the production of the spirotetronates. The recent studies reported intriguing enzymes for performing a Diels-Alder reaction, which demonstrated that VstJ catalyzes the stereoselective [4 + 2]-cycloaddition for the formation of spirotetronate structure in the versipelostatin biosynthesis (Hashimoto et al 2015), and that ChlE3 is a dialkyldecalin synthase and ChlL is a spiro-conjugate synthase in the chlorothricin biosynthesis (Tian et al 2015). These findings strongly suggest that Orf23, a homologue of VstJ and ChlL, catalyzes the formation of cyclohexene unit in the maklamicin biosynthesis and that MakC1, a ChlE3 homologue, catalyzes the formation of trans-decalin moiety.…”

Tetrodecamycin: An unusual and interesting tetronate antibiotic

“…Enzymes known to catalyze intramolecular Diels-Alder reactions have been identified. [64][65][66][67][68][69] Interestingly, the enzyme TedJ shows homology to previously identified Diels-Alderases, 70 suggesting that this protein may be responsible for formation of the decalin ring.…”