This natural product falls in the class of iridoid glycosides, which are simply monoterpenes with a glucose molecule attached.

Later in 1969, catalpol was found to be present in larger quantities in several plants in genus Rehmannia (Orobanchaceae).

Because they feed on these plants, variable checkerspot butterflies (Euphydryas chalcedona) contain high amounts of catalpol,[6] which makes them unpalatable to predators and thus serves as a defense mechanism.

[4] With iridoids stemming from a terpenoid origin, epi-iridotrial's precursor, epi-iridodial, is derived from geraniol.

[8] Addition of a glucose at carbon 1 (C1) of the iridoid backbone and oxidation of the aldehyde at C4 of epi-iridotrial produces 8-epiloganic acid.