Fungal bicyclo[2.2.2]diazaoctane indole alkaloids represent an important family of natural products with a wide-spectrum of biological activities. Although biomimetic total syntheses have been completed for representative compounds, the details of their biogenesis, especially the mechanisms for assembly of diastereomerically distinct and enantiomerically antipodal metabolites, have remained largely uncharacterized. Brevianamide A represents the most basic form of the sub-family bearing a dioxopiperazine core and a rare 3-spiro-ψ-indoxyl skeleton. Here, we identified the Brevianamide A biosynthetic gene cluster from Penicillium brevicompactum NRRL 864 and fully elucidated the metabolic pathway by gene disruption, heterologous expression, precursor incorporation experiments, and in vitro biochemical analysis. In particular, we determined BvnE as a cofactor-independent isomerase/pinacolase that is essential for selective production of Brevianamide A. Structural elucidation, molecular modeling, and mutational analysis of BvnE, and quantum chemical calculations provided critical mechanistic insights into the diastereoselective formation of the 3-spiro-ψ-indoxyl moiety in Brevianamide A. This occurs through a BvnE-controlled semi-pinacol rearrangement and a subsequent spontaneous intramolecular [4+2] hetero-Diels-Alder cycloaddition. Resolution of this 50-year old mechanistic mystery together with our recent characterization of the Diels-Alderase-mediated biogenesis of monooxopiperazines highlight the diversified biosynthetic strategies deployed by fungi for creating structurally diverse spiro-cyclized indole alkaloids.Fungal indole alkaloids bearing the unusual bicyclo[2.2.2]diazaoctane core have drawn considerable attention from natural product, synthetic and biological chemists for decades. A wealth of studies on the discovery of analogs (including semi-synthetic, synthetic and natural), biological activities and biosynthetic mechanisms have been

<p>Fungal bicyclo[2.2.2]diazaoctane indole alkaloids demonstrate intriguing structures and a wide spectrum of biological activities. Although biomimetic total syntheses have been completed for representative compounds of this structural family, the details of their biogenesis have remained largely uncharacterized. Among them, Brevianamide A represents the most basic form within this class bearing a dioxopiperazine core structure and a rare 3-<i>spiro</i>-<i>psi</i>-indoxyl skeleton. Here, we identified the Brevianamide A biosynthetic gene cluster from <i>Penicillium brevicompacticum</i> NRRL 864 and fully elucidated the metabolic pathway by targeted gene disruption, heterologous expression, precursor incorporation studies, and <i>in vitro</i> biochemical analysis. In particular, we determined that BvnE is a cofactor-independent isomerase that is essential for selective production of Brevianamide A. Based on a high resolution crystal structure of BvnE, molecular modeling, mutational analysis, and computational studies provided new mechanistic insights into the diastereoselective formation of the 3-<i>spiro</i>-<i>psi</i>-indoxyl moiety in Brevianamide A. This occurs through a biocatalyst controlled semi-Pinacol rearrangement and a subsequent spontaneous intramolecular [4+2] <i>hetero</i>-Diels-Alder cycloaddition.</p>

The rich biology associated with steroids dictates a growing demand for the new synthetic strategies that would improve the access to natural and unnatural representatives of this family. The recent advances in the field of catalysis have greatly impacted the field of natural product synthesis including the synthesis of steroids. This article provides a short overview of the recent progress in the synthesis of steroids that was enabled by the advances in catalysis.

<p>Fungal bicyclo[2.2.2]diazaoctane indole alkaloids demonstrate intriguing structures and a wide spectrum of biological activities. Although biomimetic total syntheses have been completed for representative compounds of this structural family, the details of their biogenesis have remained largely uncharacterized. Among them, Brevianamide A represents the most basic form within this class bearing a dioxopiperazine core structure and a rare 3-<i>spiro</i>-<i>psi</i>-indoxyl skeleton. Here, we identified the Brevianamide A biosynthetic gene cluster from <i>Penicillium brevicompacticum</i> NRRL 864 and fully elucidated the metabolic pathway by targeted gene disruption, heterologous expression, precursor incorporation studies, and <i>in vitro</i> biochemical analysis. In particular, we determined that BvnE is a cofactor-independent isomerase that is essential for selective production of Brevianamide A. Based on a high resolution crystal structure of BvnE, molecular modeling, mutational analysis, and computational studies provided new mechanistic insights into the diastereoselective formation of the 3-<i>spiro</i>-<i>psi</i>-indoxyl moiety in Brevianamide A. This occurs through a biocatalyst controlled semi-Pinacol rearrangement and a subsequent spontaneous intramolecular [4+2] <i>hetero</i>-Diels-Alder cycloaddition.</p>

This article describes a concise synthesis of cardiotonic steroids oleandrigenin (7) and its subsequent elaboration into the natural product rhodexin B (2) from the readily available intermediate ( 8) that could be derived from the commercially available steroids testosterone or DHEA via 3 step sequences. These studies feature an expedient installation of the β16-oxidation based on β14-hydroxyl directed epoxidation and subsequent epoxide rearrangement. The following singlet oxygen oxidation of the C17 furan moiety provides access to oleandrigenin (7) in 12 steps (LLS) and 3.9% overall yield from 8. The synthetic oleandrigenin ( 7) was successfully glycosylated with L-rhamnopyranoside-based donor using Pd(II)-catalyst, and the subsequent deprotection under acidic conditions provided cytotoxic natural product rhodexin B (2) in 68% yield (2 steps). File list (2)download file view on ChemRxiv Final Manuscript.pdf (755.58 KiB) download file view on ChemRxiv Final Supporting Information Spectra.pdf (6.08 MiB)