Synthesis and evaluation of analogs of tetracyclic <i>Ganoderma</i> alkaloids as inhibitors of the enzyme α-glucosidase

A series of synthetic analogs of tetracyclic <i>Ganoderma</i> alkaloids were prepared <i>via</i> short routes in moderate overall yields by the reaction of 3-formylchromene derivatives with enamines prepared from cyclic 1,3-dicarbonyl compounds. Single-crystal X-ray analysis of one of the tetracyclic products confirmed that they embody original tetrahydro-6<i>H</i>-chromeno[4,3-<i>b</i>]quinoline (and tetrahydrochromeno[4,3-<i>b</i>] cyclopenta[<i>e</i>]pyridine) skeletons. When tested as α-glucosidase inhibitors, these analogs proved to be up to 40 times more potent than acarbose, used as the reference inhibitor.