Molecular Decoration and Unconventional Double Bond Migration in Irumamycin Biosynthesis.

Irumamycin (Iru) is a complex polyketide with pronounced antifungal activity produced by a type I polyketide (PKS) synthase. Iru features a unique hemiketal ring and an epoxide group, making its biosynthesis and the structural diversity of related compounds particularly intriguing. In this study, we performed a detailed analysis of the biosynthetic gene cluster (BGC) to uncover the mechanisms underlying Iru formation.

Photochemistry of 2-(2-formylphenyloxy)acetic acid derivatives: synthesis of hydroxychromanones and benzofuranones.

Photochemical transformations of small molecules, such as -substituted benzaldehydes, in the absence of a photocatalyst are significantly underexplored and may reveal unexpected outcomes. In the present paper, we showed that 2-(2-formylphenoxy)acetic acid and its esters undergo photocyclization into chromanone and benzofuranone derivatives under 365 nm irradiation. The reaction occurs exclusively in dimethyl sulfoxide and can be used to efficiently obtain hydroxychromanones in good yields (27-91%).

Synthesis and biological activity of imidazole phenazine derivatives as potential inhibitors for NS2B-NS3 dengue protease.

A series of new imidazole-phenazine derivatives were synthesized via a two-step process. The condensation of 2,3-diaminophenazine and benzaldehyde derivatives proceeds with intermediate formation of an aniline Schiff base, which undergoes subsequent cyclodehydrogenation . The structures of the synthesized compounds were characterized by 1D and 2D NMR, FTIR and HRMS.

KuINins as a New Class of HIV-1 Inhibitors That Block Post-Integration DNA Repair.

Integration of HIV-1 genomic cDNA results in the formation of single-strand breaks in cellular DNA, which must be repaired for efficient viral replication. Post-integration DNA repair mainly depends on the formation of the HIV-1 integrase complex with the Ku70 protein, which promotes DNA-PK assembly at sites of integration and its activation. Here, we have developed a first-class inhibitor of the integrase-Ku70 complex formation that inhibits HIV-1 replication in cell culture by acting at the stage of post-integration DNA repair.

Synthesis of chroman-annulated cyclopropanols photoinduced intramolecular [2 + 1]-cycloaddition of 2-allyloxybenzaldehydes.

2-Allyloxybenzaldehydes undergo [2 + 1] cycloadditions under 365 nm LED irradiation to form the corresponding chroman-fused cyclopropanols. The reaction proceeds easily without any catalysts or additives in dimethyl sulfoxide.

Merging Johnson-Claisen and Aromatic Claisen [3,3]-Sigmatropic Rearrangements: Ytterbium Triflate/2,6-Di--butylpyridine Catalytic System.

General synthetic approach toward phenols with a polyfunctional side-chain is described. It is based on two subsequent [3,3]-sigmatropic rearrangements, in particular, Johnson-Claisen and aromatic Claisen. Facilitation of the reaction sequence is achieved by the separation of steps and discovery of the efficient catalysts for aromatic Claisen rearrangement.

Convergent Assembly of the Tricyclic Labdane Core Enables Synthesis of Diverse Forskolin-like Molecules.

We report a new synthetic strategy for the flexible preparation of forskolin-like molecules. The approach is different from the previously published works and employs a convergent assembly of the tricyclic labdane-type core from pre-functionalized cyclic building blocks. Stereoselective Michael addition enabled the fragment coupling with excellent control over three newly created contiguous stereocenters, all-carbon quaternary centers included.

[1,5]-Hydride Shift Triggered -Dealkylative Cyclization into 2-Oxo-1,2,3,4-tetrahydroquinoline-3-carboxylates via Boronate Complexes.

A new simple one-pot two-step protocol for the synthesis of 2-oxo-1,2,3,4-tetrahydroquinoline-3-carboxylate from 2-(2-(benzylamino)benzylidene)malonate under the action of BF3·Et2O was developed. It was shown that the reaction proceeds through the formation of a stable iminium intermediate containing a difluoroboryl bridge in the dicarbonyl fragment of the molecule.

Short Synthesis of (+)-Actinobolin: Simple Entry to Complex Small-Molecule Inhibitors of Protein Synthesis.

We report a concise synthesis of the naturally occurring protein synthesis inhibitor (+)-actinobolin (1). The densely functionalized and stereochemically complex molecular structure of 1 was assembled from (-)-quinic acid, L-threonine, and L-alanine as the principal components. Our route is based around a convergent strategy that features conjugate addition of an α-amino radical in the key fragment-coupling step.

Disclosing biosynthetic connections and functions of atypical angucyclinones with a fragmented C-ring.

This review on atypical angucyclinones possessing an aromatic cleavage of the C-ring covers literature between 1995 and early 2020.The unusual framework of the middle C-ring, "broken" as a result of biotransformations and oxidations in vivo and bearing an sp-C connection, is of interest for biosynthetic investigations. The reported 39 natural compounds (55 including stereoisomers) have been analyzed and arranged into three structural groups.

Imidazol-5-one as an Acceptor in Donor-Acceptor Cyclopropanes: Cycloaddition with Aldehydes.

Spiro[imidazol-5-one-4,1'-cyclopropanes] behave as donor-acceptor (D-A) cyclopropanes in a formal cycloaddition reaction with aldehydes. The activation of such type of cyclopropanes is achieved with an equivalent of Brønsted acid. The reaction proceeds in high yields of 51-92% and demonstrates moderate diastereoselectivity at the quaternary stereocenter, which is determined by the electron-donating nature of the aldehyde partner.

Nitroacetic Esters in the Regioselective Synthesis of Isoxazole-3,5-dicarboxylic Acid Derivatives.

An efficient and high-yielding strategy to prepare "unsymmetrical" 4-aryl-isoxazol-3,5-dicarboxylic acid derivatives from nitroacetic esters and aromatic aldehydes has been developed. The strategy is based on the isolation and usage of the previously missed intermediate of the Dornow reaction-5-hydroxy-6-oxo-4-aryl-6-1,2-oxazine-3-carboxylates. In addition, the mechanism of the Dornow reaction was partially revised.

Sigmatropic Rearrangement-Based Synthesis of 4-Alkenyl-1,3-dithiol-2-ones.

A series of conjugated 4-alkenyl-1,3-dithiol-2-ones have been prepared by microwave-assisted rearrangement of S-(4-acyloxy-2-alkynyl)- O-ethyl xanthates in moderate to good yields. The synthetic approach is based on a combination of [3,3] and [1,5] sigmatropic rearrangements as well as the intermediacy of a reactive betaine that induces the ionic elimination of the acyloxy group. The [1,5] sigmatropic rearrangement was confirmed by a deuterium-labeling experiment.

A Planar-Chiral Rhodium(III) Catalyst with a Sterically Demanding Cyclopentadienyl Ligand and Its Application in the Enantioselective Synthesis of Dihydroisoquinolones.

The rapid development of enantioselective C-H activation reactions has created a demand for new types of catalysts. Herein, we report the synthesis of a novel planar-chiral rhodium catalyst [(C H Bu CH Bu)RhI ] in two steps from commercially available [(cod)RhCl] and tert-butylacetylene. Pure enantiomers of the catalyst were obtained through separation of its diastereomeric adducts with natural (S)-proline.

Extension to the Silyl-Tethered Radical Cyclization: Cyclohex-2-en-1-oxy Vinyl Silanes in Stereoselective Radical Addition/Cyclization Cascades.

A novel radical cascade reaction of xanthates with 1-[(vinyldimethylsilyl)oxy]cyclohex-2-enes is developed. Due to the steric and electronic differentiation of the two olefinic functions, exclusive regioselectivity and high stereoselectivity of the addition-cyclization are observed. Several methods for modification of both the silicon tether and the xanthate function are reported.