Sc(OTf)3-catalyzed one-pot ene-Prins cyclization: a novel synthesis of octahydro-2H-chromen-4-ols

Catalytic synthesis of bioactive 2H-chromene alcohols from (−)-isopulegol and acetone on sulfonated clays

Condensation of (−)-isopulegol with acetone was investigated at 25–40 °C over clay based materials (K10, cloisite Na+ and halloysite nanotubes) modified with sulfonic acid groups by one-pot sulfonation with chlorosulfonic acid or via organosilylation with 2-(4-chlrosulfonylphenyl)-ethyltrimethoxysilane. The target product was the R diastereomer of dimethyl-substituted octahydro-2H-chromen-4-ol with exhibits antiviral activity. The catalysts were characterized by a range of physico-chemical methods. The effect of the initial isopulegol concentrations on the yield of ketone-derived chromenols and the R/S isomers ratio was studied for the first time. The best catalyst was a highly acidic, large pore K10-clay modified by sulfonic acid. Varying the initial concentration of the reagents allows to find a balance between dehydration by-products and a side etherification reaction. A high yield (73%) of the desired chromenols was reached using 0.52 mol/l initial (−)-isopulegol concentration after 240 min at 87% substrate conversion and reaction temperature 25 °C. The yield exceeded that of other previously reported in the open literature catalysts.

A Novel Class of Tyrosyl-DNA Phosphodiesterase 1 Inhibitors That Contains the Octahydro-2H-chromen-4-ol Scaffold

Tyrosyl-DNA phosphodiesterase 1 (Tdp1) is a DNA repair enzyme that mends topoisomerase 1-mediated DNA damage. Tdp1 is a current inhibition target for the development of improved anticancer treatments, as its inhibition may enhance the therapeutic effect of topoisomerase 1 poisons. Here, we report a study on the development of a novel class of Tdp1 inhibitors that is based on the octahydro-2H-chromene scaffold. Inhibition and binding assays revealed that these compounds are potent inhibitors of Tdp1, with IC50 and KD values in the low micromolar concentration range. Molecular modelling predicted plausible conformations of the active ligands, blocking access to the enzymatic machinery of Tdp1. Our results thus help establish a structural-activity relationship for octahydro-2H-chromene-based Tdp1 inhibitors, which will be useful for future Tdp1 inhibitor development work.

A Novel Sc(OTf)3 -Catalyzed (2+2+1)-Cycloannulation/Aza-Friedel-Crafts Alkylation Sequence toward Multicyclic 2-Pyrrolines

The rapid assembly of molecular complexity continues to be at the forefront of novel reaction development. In the pursuit of that goal, we herein report a novel Sc(OTf)₃ -catalyzed, one-pot multicomponent reaction that furnishes complex multicyclic 2-pyrrolines with excellent overall yields and perfect diastereocontrol. This process is based on our previously established (2+2+1)-cycloannulation of in situ generated 1-azaallyl cations, 1,3-dicarbonyls and primary amines. The newly formed and highly reactive aminal moiety is readily substituted with indoles and pyrroles both as external and internal π-nucleophiles to provide densely functionalized N-heterocycles with four new σ-bonds and two vicinal quaternary stereogenic centers. In addition, DFT calculations have been conducted to further characterize the intermediate 1-azaallyl cations.

Highly potent activity of isopulegol-derived substituted octahydro-2H-chromen-4-ols against influenza A and B viruses

A set of (-)-isopulegol derived octahydro-2H-chromen-4-ols was synthesized and evaluated in vitro for antiviral activity against panel of reference influenza virus strains differing in subtype, origin (human or avian) and drug resistance. Compound (4R)-11a produced via one-pot synthesis by interaction between (-)-isopulegol and acetone was found to exhibit an outstanding activity against a number of H1N1 and H2N2 influenza virus strains with selectivity index more than 1500. (4R)-11a was shown to be most potent at early stages of viral cycle. Good correlation between anti-viral activity and calculated binding energy to hemagglutinin TBHQ active site was demonstrated.

One-step, stereoselective synthesis of octahydrochromanes via the Prins reaction and their cannabinoid activities

Novel, functionalized octahydrochromene derivatives were synthesized in a single step via the Prins reaction. Enantiomerically pure (+)-isopulegol was reacted with benzaldehyde to stereoselectively yield the corresponding octahydro-2H-chromen-4-ol derivative containing five stereocenters. A total of 10 compounds were synthesized by altering the enantiomer of isopulegol and the substituted benzaldehyde, and the resulting enantiopure octahydrochromenes were screened in vitro against the cannabinoid receptor isoforms CB1 and CB2. Compounds containing an olefin at the C4 position [(+)-3c, (-)-3c, (-)-7c, (-)-9c and (-)-11c] of the octahydrochromene scaffold were found to exhibit reasonable displacement of [3H] CP55,940 from the CB receptors, whereas the corresponding hydroxy analogs [(+)-3a, (+)-3b, (-)-3a, (-)-3b and (+)-5a] had very little or no effect.

Stereoselective synthesis of protected l- and d-dideoxysugars and analogues via Prins cyclisations

A de novo approach for the rapid construction of orthogonally protected l- and d-deoxysugars and analogues is described. A novel and robust silicon-acetal undergoes Prins cyclisations with a series of homoallylic alcohols in high yield and excellent stereocontrol. Modified Tamao-Fleming oxidation of the resulting silyltetrahydropyrans gives direct access to deoxyglycoside analogues and the approach was showcased in the synthesis of protected l-oliose, a component of the anticancer agent aclacinomycin A.

Synthesis of isochromene-type scaffolds via single-flask Diels-Alder-[4 + 2]-annulation sequence of a silyl-substituted diene with menadione

A sequential Diels-Alder reaction/silicon-directed [4 + 2]-annulation was developed to assemble hydroisochromene-type ring systems from menadione 2. In the first step, a Diels-Alder of the 1-silyl-substituted butadiene 1 with 2 furnished an intermediate cyclic allylsilane. Subsequently, TMSOTf promoted a [4 + 2]-annulation through trapping of an oxonium, generated by condensation between an aldehyde and the TBS protected alcohol resulted in the formation of a cis-fused hydroisochromene 13.