4-Hydroxycoumarins

Dicoumarol appears in spoiled silage of sweet clover and is considered a natural mycotoxin substance of combined plant and fungal origin.

The synthetic drugs in the 4-hydroxycoumarin class are all noted primarily for their use as anticoagulants, though they can have several additional effects.

The simplest synthetic molecule in the 4-hydroxycoumarin class is warfarin, in which the aromatic 3-position substituent is a simple phenyl group.

The second generation agents have even larger lipid-soluble substituents at the 3-position (e.g. brodifacoum), a chemical change that causes their half-lives in the body to be greatly increased (sometimes to months).

The second-generation vitamin K antagonist agents, used only in this fashion as poisons (because their duration of action is too long to be used as pharmaceuticals) include:

Warning label on a tube of "brown rat" poison laid on a dike of the Scheldt river in Steendorp, Belgium. The tube contains bromadiolone , a second-generation ("super-warfarin") anticoagulant. The label in Dutch states, in part: Contains an anticoagulant with prolonged activity. Antidote Vitamin K1.
Mechanism of action for K1-vitamin.