Inspired by naturally occurring bis-isochromans such as penicisteckins, we envisaged the first synthesis of biaryl-type bis-1-arylisochromans containing a stereogenic ortho-trisubstituted biaryl axis. We achieved the stereoselective synthesis of 5,5′-linked heterodimeric bis-isochromans containing both central and axial chirality elements by performing diastereoselective Suzuki–Miyaura biaryl coupling reactions on two optically active 1-arylpropan-2-ol derivatives, followed by two oxa-Pictet–Spengler cyclizations with aryl aldehydes or methoxymethyl chloride. We studied the diastereoselectivity of the cyclization step, separated the stereoisomeric products with chiral preparative HPLC and determined the absolute configuration through a combination of vibrational circular dichroism (VCD), NMR and single-crystal X-ray diffraction analysis. We demonstrated that different aryl groups could be introduced into the two isochroman subunits, since the dimethoxyaryl subunit reacted faster, enabling the two oxa-Pictet–Spengler cyclizations to be performed separately with different aryl aldehydes. We also explored the acid-catalyzed isomerization and oxidation to axially chiral ortho-quinones in order to produce stereoisomeric and oxidized analogs, respectively. We identified the antibacterial activity of our target bis-isochromans against Bacillus subtilis and Enterococcus faecalis with minimum inhibitory concentrations down to 4.0 and 0.5 μg/mL, respectively, which depend on the stereochemistry and substitution pattern of the bis-isochroman skeleton.

Glycosaminoglycans (GAGs) are linear, high molecular weight polydisperse heteropolysaccharides consisting of repeating disaccharide units, which always contain a uronic acid building block (e.g., d-glucuronic acid or l-iduronic acid). Their analogues containing d-mannuronic acid were not known until now. Another important class of the linear negatively charged polisaccharides are alginates, which are also present in the cell surface in the cell wall. They are composed of blocks of 1,4-linked β-d-mannuronic acid and its C-5 epimer α-l-guluronic acid in alternating or random order. Both groups of molecules have significant biological activity (e.g., cell growth inhibitory activity, anti-inflammatory effect, etc.). In the course of our research, we combined the structural characteristics of these two groups of molecules and produced a series of heparan sulphate analogue trisaccharides containing d-mannuronic acid, with a simplified structure, in which α- and β-mannosidic bonds are also found. Since trisaccharides may exert diverse biological effects and alginate derivatives can influence wound healing processes, we investigated the effects of the synthesized compounds on primary human dermal fibroblasts. We found that, when applied at 10 μM, none of the compounds influenced viability or spontaneous collagen production; however, some derivatives exhibited anti-inflammatory activity and suppressed the poly(I:C)-induced release of interleukin 6.

A simplified molecular-dynamics-based electronic circular dichroism (ECD) approach was tested on three condensed derivatives with limited conformational flexibility and an isochroman-2H-chromene hybrid, the ECD spectra of which could not be precisely reproduced by the conventional ECD calculation protocol. Application of explicit solvent molecules at the molecular mechanics (MD) level in the dynamics simulations and subsequent TDDFT-ECD calculation for the unoptimized MD structures was able to improve the agreements between experimental and computed spectra. Since enhancements were achieved even for molecules with limited conformational flexibility, deformations caused by the solvent molecules and multitudes of conformers produced with unoptimized geometries seem to be key factors for better agreement. The MD approach could confirm that aggregation of the phenanthrene natural product luzulin A had a significant contribution to a specific wavelength range of the experimental ECD. The MD approach has proved that dimer formation occurred in solution and this was responsible for the anomalous ECD spectrum. The scope and limitations of the method have also been discussed.