Expanding Diversity without Protecting Groups: (+)-Sclareolide to Indolosesquiterpene Alkaloid Mycoleptodiscin A and Analogues

Microbe Engineering to Provide Drimane-Type Building Blocks for Chiral Pool Synthesis of Meroterpenoids

Drimane-type merosesquiterpenoids (DMT) are a class of natural products with diverse structures and broad biological activity. Classical DMT synthesis relies on atom-inefficient plant-derived chiral pool building blocks, while alternative drimane-type building blocks such as drimenol and albicanol offer more direct routes but face production challenges. In this study, we engineered a microbial platform for efficient production of these building blocks. By optimizing the PhoN-IPK system through rational engineering and incorporating a Nudix hydrolase, we achieved a drimenol production of 398 mg/L and high albicanol titers of 1805 mg/L in shake flasks and 3.5 g/L in a bioreactor. Structural analysis and molecular dynamics simulations of the engineered PhoN provided insights into its improved catalytic efficiency. We demonstrated the utility of this platform by synthesizing several DMT using albicanol as the starting material, reducing the number of synthetic steps and improving overall efficiency as compared to classical approaches.

Synthesis of drimanyl indole fragments of drimentine alkaloids and their antibacterial activities

Two types of drimanyl indole fragments of drimentine alkaloids were synthesized and evaluated their in vitro antibacterial activities using minimum inhibitory concentration. Analysis of structure-activity relationship against Ralstonia solanacearum revealed that fragment I exhibited superior inhibitory activity compared to fragment II. Notably, free NH of the indole motif was essential for antibacterial activity, while C12OH of the drimane skeleton was beneficial for enhancing the inhibitory effect. Compound 2, possessing these structural features, showed the highest activity to R. solanacearum among all the tested compounds with a MIC value of 8 µg/mL, indicating its potential as a promising lead for the development of novel antibiotics.

Modular Synthesis and Antimicrobial Investigation of Mycoleptodiscin A and Simplified Indolosesquiterpenoids

The structure-activity relationship of the unusual indolosesquiterpenoid mycoleptodiscin A is unknown due to natural scarcity and inefficient synthesis. A modular approach leveraging Larock indole synthesis has been established to access mycoleptodiscin A and a divergent collection of drimenyl indoles. It features the utilization of an inexpensive (+)-sclareolide, modularity, purification-economy, and scalability, which facilitates the first biological evaluation of mycoleptodiscin A and related precursors.

Unified short syntheses of oxygenated tricyclic aromatic diterpenes by radical cyclization with a photoredox catalyst

The biomimetic two-phase strategy employing polyene cyclization and subsequent oxidation/substitution is an effective approach for divergent syntheses of [6-6-6]-tricyclic diterpenes. However, this strategy requires lengthy sequences for syntheses of oxygenated tricyclic aromatic abietane/podocarpane diterpenes owing to the many linear oxidation/substitution steps after cyclization. Here, we present a new synthetic route based on a convergent reverse two-phase strategy employing a reverse radical cyclization approach, which enabled the unified short syntheses of four aromatic abietane/podocarpane diterpenes and the divergent short syntheses of other related diterpenes. Oxygenated and substituted precursors for cyclization were convergently prepared through Friedel-Crafts acylation and rhodium-catalyzed site-selective iodination. Radical redox cyclization using an iridium photoredox catalyst involving neophyl rearrangement furnished the thermodynamically favored 6-membered ring preferentially. (±)-5,6-Dehydrosugiol, salvinolone, crossogumerin A, and Δ5-nimbidiol were synthesized in only 8 steps. An oxygenated cyclized intermediate was also useful for divergent derivatization to sugiol, ferruginol, saprorthoquinone, cryptomeriololide, and salvinolone.

Asymmetric Domino Heck/Dearomatization Reaction of β-Naphthols to Construct Indole-Terpenoid Frameworks

A palladium-catalyzed enantioselective Heck cyclization/dearomatization cascade via capturing the cyclized Heck π-allylpalladium intermediate by β-naphthols is reported, which provides a new strategy for the construction of chiral indole-terpenoid frameworks. This method affords indole-functionalized β-naphthalenone compounds bearing an all-carbon-substituted quaternary chiral center in excellent yields (up to 92%) and enantioselectivities (up to 94% ee). In addition, the utility of this method is showcased by the gram-scale syntheses and diverse transformations of the dearomatized products.

Synthesis of Asthma Drug Zafirlukast (Accolate) Using Intramolecular Oxidative Coupling via sp3 C-H Bond Activation

The FDA-approved drug for the treatment of asthma, zafirlukast, is synthesized engaging multiple catalytic reactions including a new method for the construction of 3-aroylindoles via oxidative cyclization. The highlights include transition-metal and peroxide free C-H bond activation using the stoichiometric amount of sodium persulfate as an oxidizing agent in the construction of 3-aroylindole, avoiding transition metal, with over 28% overall yield. The complete process has a turnaround time of 28 h to get the target molecule starting from substituted aniline, with practically no protecting groups.

Biomimetic Enantioselective Total Synthesis of (-)-Petromindole

The first enantioselective total synthesis of (-)-petromindole, an architecturally distinct congener of indole diterpene family, has been achieved. Key features of this synthetic route include the scalable and concise synthesis of tricyclic allylic alcohol from enantiopure Wieland-Mischer ketone derivative, and TMSOTf-mediated, highly efficient biomimetic C-4 cyclization of indole derivative for the rapid construction of a hexacyclic skeleton of petromindole.

Regiodivergent Remote Arylation of Cycloalkanols to Dysideanone's Fused Carbotetracycles and Its Bridged Isomers

Regiodivergent γ and γ' arylations across an all-carbon quaternary center of cycloalkanols to access enantioenriched fused and bridged carbotetracycles are reported. The conformation of the carbocation guided either sequential stereospecific β-C-Me/γ-C-H-shifts or β-C-Me/γ'-C-H-shifts, providing fused carbotetracyclic analogs of dysideanone or bridged tetracycles, respectively. The reaction is highly stereoselective in building three contiguous stereocenters, where one, two, or three could be all-carbon quaternary centers. Interestingly, mechanistic studies revealed a crucial role of a methyl substituent in controlling regioselectivity.

Bioactivity-guided mixed synthesis accelerate the serendipity in lead optimization: Discovery of fungicidal homodrimanyl amides

The bioactivity-guided mixed synthesis was conceived, in which the designed mix-reactions were run in parallel for simultaneous construction of different kinds of analogs. The valuable ones were protruded by biological screening. This tactic will facilitate more rapid incorporation of bioactive candidates into pesticide chemists' repertoire, exemplified by the optimization of less explored homodrimanes as antifungal ingredients. The discovery of D9 as a potent fungicidal agent can be completed in <2 weeks by one student, with EC₅₀ of 3.33 mg/L and 2.45 mg/L against S. sclerotiorum and B. cinerea, respectively. To confirm the practicability, time-efficiency, and reliability, specific homodrimanes (82 derivatives) were synthesized and elucidated separately and determined for EC₅₀ values. The SAR correlated well with the intentionally mixed synthesis and the potential was further confirmed by the in vivo bioassay. This methodology will foster more efficient exploration of biologically relevant chemical space of natural products in pesticide discovery, and can also be tailored readily for the lead optimization in medicinal chemistry.