Cardenolide

Cardenolides are a type of steroids. Many plants contain cardenolides in the form of cardenolide glycosides (i.e. cardenolides that contain structural groups derived from sugars; see "Glycoside"). Cardenolides are toxic (specifically, heart-arresting).

Etymology

Supposedly, the term derives from Greek kardiā, "heart". It shouldn't be confused with "cardanolides". Cardanolides are a class of steroids (or aglycones if viewed as cardiac glycoside constituents), and cardenolides are a subtype of this class (see ).

Structure

Cardenolides are C(23)-steroids with methyl groups at C-10 and C-13 and a five-membered lactone at C-17. They are aglycone constituents of cardiac glycosides and must have at least one double bond in the molecule. The class includes cardadienolides and cardatrienolides. Members include:
*digitoxin
*acetyldigitoxins
*digitoxigenin
*digoxin
*acetyldigoxins
*digoxigenin
*medigoxin
*strophanthins
*cymarine
*ouabain
*strophanthidin

As defense mechanism

Some plant and animal species use cardenolides as a defense mechanism, most notably the monarch butterflies. Adult monarch butterflies store the cardenolides they have built-up as larvae feeding mostly on milkweeds ("Asclepias"). The cardenolide content in butterflies deters vertebrate predators, with some exceptions of cardenolide-tolerant predators like black-backed orioles ("Icterus abeillei" Lesson) and black headed grosbeaks ("Pheucticus melanocephalus" Swainson) that account for 60% of monarch butterfly mortalities in the overwintering sites in central Mexico.

See also

Bufadienolide

Cardiac glycoside