Compds. incorporating various elements of the 3,4’-bis(piperidine) core assocd. with the sponge-derived alkaloid haliclonacyclamine A (HA), have been prepd. through, inter alia, aldol-type reactions of N-substituted piperidin-4-ones and certain derivs. Screening of these compds. in various assays, including an ecol. one, reveals that compd. I exhibits allelochem. properties similar to those assocd. with HA itself.