Synthesis and HPLC-ECD Study of Cytostatic Condensed <i>O,N</i>-Heterocycles Obtained from 3-Aminoflavanones

Racemic chiral <i>O,N</i>-heterocycles containing 2-arylchroman or 2-aryl-2<i>H</i>-chromene subunit condensed with morpholine, thiazole, or pyrrole moieties at the C-3-C-4 bond were synthesized with various substitution patterns of the aryl group by the cyclization of <i>cis</i>- or <i>trans</i>-3-aminoflavanone analogues. The 3-aminoflavanone precursors were obtained in a Neber rearrangement of oxime tosylates of flavanones, which provided the <i>trans</i> diastereomer as the major product and enabled the isolation of both the <i>cis</i>- and <i>trans</i>-diastereomers. The <i>cis</i>- and <i>trans</i>-aminoflavanones were utilized to prepare three diastereomers of 5-aryl-chromeno[4,3-b][1,4]oxazines. Antiproliferative activity of the condensed heterocycles and precursors was evaluated against A2780 and WM35 cancer cell lines. For a 3-(<i>N</i>-chloroacetylamino)-flavan-4-ol derivative, showing structural analogy with acyclic acid ceramidase inhibitors, 0.15 μM, 3.50 μM, and 6.06 μM IC₅₀ values were measured against A2780, WM35, and HaCat cell lines, and apoptotic mechanism was confirmed. Low micromolar IC₅₀ values down to 2.14 μM were identified for the thiazole- and pyrrole-condensed 2<i>H</i>-chromene derivatives. Enantiomers of the condensed heterocycles were separated by HPLC using chiral stationary phase, HPLC-ECD spectra were recorded and TDDFT-ECD calculations were performed to determine the absolute configuration and solution conformation. Characteristic ECD transitions of the separated enantiomers were correlated with the absolute configuration and effect of substitution pattern on the HPLC elution order was determined.