1-Nicotinoylbenzotriazole: A Convenient Tool for Site-Selective Protection of 5,7-Dihydroxycoumarins

Bioinspired Pyrano[2,3-f]chromen-8-ones: Ring C-Opened Analogues of Calanolide A: Synthesis and Anti-HIV-1 Evaluation

We have designed and synthesized a series of bioinspired pyrano[2,3-f]coumarin-based Calanolide A analogs with anti-HIV activity. The design of these new calanolide analogs involved incorporating nitrogen heterocycles or aromatic groups in lieu of ring C, effectively mimicking and preserving their bioactive properties. Three directions for the synthesis were explored: reaction of 5-hydroxy-2,2-dimethyl-10-propyl-2H,8H-pyrano[2,3-f]chromen-8-one with (i) 1,2,4-triazines, (ii) sulfonylation followed by Suzuki cross-coupling with (het)aryl boronic acids, and (iii) aminomethylation by Mannich reaction. Antiviral assay of the synthesized compounds showed that compound 4 has moderate activity against HIV-1 on enzymes and poor activity on the cell model. A molecular docking study demonstrates a good correlation between in silico and in vitro HIV-1 reverse transcriptase (RT) activity of the compounds when docked to the nonnucleoside RT inhibitor binding site, and alternative binding modes of the considered analogs of Calanolide A were established.

Coumarin-pyridine push-pull fluorophores: Synthesis and photophysical studies

A series of coumarin-pyridine-based push-pull fluorophores were prepared starting from 1,2,4-triazines by using direct C-H functionalization (S_N^H-reaction)-Diels-Alder-retro Diels-Alder domino reaction sequence. This efficient synthetic strategy allowed to obtain a series of 19 coumarin-pyridine fluorophores. Their photophysical properties were studied. While pyridine-substituted derivatives of 4-alkylcoumarins may be considered as alternative to coumarin dyes characterized by emission maxima mainly in a visible region with wavelengths of 402-415 nm, absorption in the UV range at 210-307 nm, and good photoluminescence quantum yields of 6-19%, all the derivatives of 4-phenylcoumarin did not exhibit any noticeable fluorescence. More detailed photophysical studies were carried out for two the most representative derivatives of 4-alkyl-coumarin-pyridines to demonstrate their positive solvatochromism, and the collected data were analyzed by using Lippert-Mataga equation, as well as Kosower and Dimroth/Reichardt scales. The obtained results demonstrate that the combining two chromophore systems, such as 2,5-diarylpyridine and coumarin ones, is promising in terms of improving the photophysical properties of the new coumarin-pyridine hybrid compounds.

Site-selective acylation of natural products with BINOL-derived phosphoric acids

The site-selective acylation of a steroidal natural product 19-hydroxydehydroepiandrosterone catalyzed by 1,1'-Bi(2-napthol)-derived (BINOL) chiral phosphoric acids (CPA's) is described. Systematic variation and multivariate linear regression analysis reveal that the same steric parameters typically needed for high enantioselectivity with this class of CPAs are also required for site-selectivity in this case. Density functional theory calculations identify additional weak CH-π interactions as contributors to site discrimination. We further report a rare example of site-selective acylation of phenols through the evaluation of naringenin, a flavonoid natural product, using CPA catalysis. These results suggest that BINOL-derived CPA's may have broader applications in site-selective catalysis.