Calyculins are natural products originally isolated from the marine sponge Discodermia calyx.

[2] Calyculins have proven to be strong serine/threonine protein phosphatase inhibitors and based on this property, calyculins might be potential tumor-promoting agents.

A laboratory synthesis of calyculin A has been reported.

[3] Calyculin A is biosynthesized as a pyrophosphate containing phosphocalyculin A protoxins by a hybrid PKS-NRPS pathway within the sponge bacterial symbiont, "Candidatus Entotheonella" sp.

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