Biomimetic Synthetic Studies on the Bruceol Family of Meroterpenoid Natural Products

A bioinspired, one-step total synthesis of peshawaraquinone

A concise synthesis of a stereochemically complex meroterpenoid, peshawaraquinone, via the unsymmetrical dimerization of its achiral precursor, dehydro-α-lapachone, is reported. Enabled by reversible oxa-6π-electrocyclizations of 2H-pyran intermediates, the base-catalyzed dimerization sets up an intramolecular (3 + 2) cycloaddition, with the formation of six stereocenters during the cascade. Combining the generation and in situ dimerization of dehydro-α-lapachone allows a one-step total synthesis of peshawaraquinone from lawsone and prenal.

[2 + 2]-Cycloaddition-derived cyclobutane natural products: structural diversity, sources, bioactivities, and biomimetic syntheses

This review summarizes the structural diversity, bioactivities, and biomimetic synthesis of [2 + 2]-type cyclobutane natural products, along with discussion of their biosynthesis, stereochemical analysis, racemic occurrence, and biomimetic synthesis.

Sesquiterpenoids from Seriphidium transiliense and Their Melanogenic Activity

A sesquiterpenoid with an unprecedented 5/5/4 tricyclic skeleton (1), a nor-sesquiterpenoid with a rare 6/7 bicyclic skeleton (2), 10 new sesquiterpenoids (3-12), and six known analogues (13-18) were isolated from the whole plants of Seriphidium transiliense. The structures of compounds 1-12 were elucidated by spectroscopic data analysis. Compound 7 showed melanogenic promotion activity in murine melanoma (B16) cells more potent than the positive control used, 8-methoxypsoralen (8-MOP). Further mechanistic studies indicated that compound 7 promotes melanogenesis through activating the transcription of microphthalmia-associated transcription factor (MITF) and tyrosinase family genes in B16 cells. Moreover, compound 7 also inhibited the expression of IFN-γ-chemokine through the JAK/STAT signaling pathway in immortalized human keratinocyte (HaCaT) cells. These results suggest that the sesquiterpenoid 7 shows potential activity for treating vitiligo.

Recent advances in the synthesis of natural products containing the phloroglucinol motif

Covering: June 2009 to 2021Natural products containing a phloroglucinol motif include simple and oligomeric phloroglucinols, polycyclic polyprenylated acylphloroglucinols, phloroglucinol-terpenes, xanthones, flavonoids, and coumarins. These compounds represent a major class of secondary metabolites which exhibit a wide range of biological activities such as antimicrobial, anti-inflammatory, antioxidant and hypoglycaemic properties. A number of these compounds have been authorized for therapeutic use or are currently being studied in clinical trials. Their structural diversity and utility in both traditional and conventional medicine have made them popular synthetic targets over the years. In this review, we compile and summarise the recent synthetic approaches to the natural products bearing a phloroglucinol motif. Focus has been given on ingenious strategies to functionalize the phloroglucinol moiety at multiple positions. The isolation and bioactivities of the compounds are also provided.

Recent Advances in Divergent Synthetic Strategies for Indole-Based Natural Product Libraries

Considering the potential bioactivities of natural product and natural product-like compounds with highly complex and diverse structures, the screening of collections and small-molecule libraries for high-throughput screening (HTS) and high-content screening (HCS) has emerged as a powerful tool in the development of novel therapeutic agents. Herein, we review the recent advances in divergent synthetic approaches such as complexity-to-diversity (Ctd) and biomimetic strategies for the generation of structurally complex and diverse indole-based natural product and natural product-like small-molecule libraries.

Natural product anticipation through synthesis

Natural product synthesis remains one of the most vibrant and intellectually rewarding areas of chemistry, although the justifications for pursuing it have evolved over time. In the early years, the emphasis lay on structure elucidation and confirmation through synthesis, as exemplified by celebrated studies on cocaine, morphine, strychnine and chlorophyll. This was followed by a phase where the sheer demonstration that highly complex molecules could be recreated in the laboratory in a rational manner was enough to justify the economic expense and intellectual agonies of a synthesis. Since then, syntheses of natural products have served as platforms for the demonstration of elegant strategies, for inventing new methodology 'on the fly' or to demonstrate the usefulness and scope of methods established with simpler molecules. We now add another aspect that we find fascinating, viz. 'natural product anticipation'. In this Review, we survey cases where the synthesis of a compound in the laboratory has preceded its isolation from nature. The focus of our Review lies on examples where this anticipation of a natural product has triggered a successful search or where synthesis and isolation have occurred independently. Finally, we highlight cases where a potential natural product structure has been suggested as a result of synthetic endeavours but not yet confirmed by isolation, inviting further collaborations between synthetic and natural product chemists.

Bio-inspired construction of a tetracyclic ring system with an avarane skeleton: total synthesis of dactyloquinone A

We report the asymmetric construction of an avarane skeleton. The strategy involves a Lewis acid-catalyzed cyclization reaction, which drives the methyl groups of two different configurations at the C-4 site to migrate by 1, 2-rearrangement.

Bioinspired syntheses of cryptoflavanones C and D, oboflavanones A and B, and cryptoyunnanones G and H enabled by an acid-triggered cascade sequence

Collective total syntheses of oboflavanones A-B, cryptoflavanones C-D, and cryptoyunnanones G-H via a bioinspired acid-triggered olefin isomerization/hemiacetalization/dehydration/formal [3 + 3]-type cycloaddition cascade process are presented.

Peculiarities of meroterpenoids and their bioproduction

Meroterpenoids are a class of terpenoid-containing hybrid natural products with impressive structural architectures and remarkable pharmacological activities. Remarkable advances in enzymology and synthetic biology have greatly contributed to the elucidation of the molecular basis for their biosynthesis. Here, we review structurally unique meroterpenoids catalyzed by novel enzymes and unusual enzymatic reactions over the period of last 5 years. We also discuss recent progress on the biomimetic synthesis of chrome meroterpenoids and synthetic biology-driven biomanufacturing of tropolone sesquiterpenoids, merochlorins, and plant-derived meroterpenoid cannabinoids. In particular, we focus on the novel enzymes involved in the biosynthesis of polyketide-terpenoids, nonribosomal peptide-terpenoids, terpenoid alkaloids, and meroterpenoid with unique structures. The biological activities of these meroterpenoids are also discussed. The information reviewed here might provide useful clues and lay the foundation for developing new meroterpenoid-derived drugs. KEY POINTS: • Meroterpenoids possess intriguing structural features and relevant biological activities. • Novel enzymes are involved in the biosynthesis of meroterpenoids with unique structures. • Biomimetic synthesis and synthetic biology enable the construction and manufacturing of complex meroterpenoids.

Isolation and Biomimetic Oxidation of Prenylbruceol A, an Anticipated Meroterpenoid Natural Product from Philotheca myoporoides

Reinvestigation of the coumarin meroterpenoids of Philotheca myoporoides using pressurized hot water extraction (PHWE) procedures led to the isolation of prenylbruceol A, a proposed biosynthetic precursor of seven previously reported bruceol derivatives, prenylbruceols B-H. Protobruceol-I, ostruthin, dipetalactone, and a new dihydrocoumarin natural product were isolated alongside prenylbruceol A. A biomimetic singlet oxygen ene reaction of prenylbruceol A allowed the semisynthesis of prenylbruceols B, C, and D.