What cyanogenic compound gives bitter almonds their poisoning risk?

The cyanogenic compound that gives bitter almonds their poisoning risk is amygdalin.

Amygdalin is a cyanogenic glycoside concentrated in the seeds or kernels of several Prunus fruits, including bitter almonds, apricots, peaches, cherries and plums. When plant tissue is crushed or chewed, enzymes can break amygdalin down into glucose, benzaldehyde and hydrogen cyanide. The cyanide is responsible for the serious poisoning risk, while benzaldehyde contributes to the characteristic bitter almond aroma and flavour.

Bitter almonds contain far more amygdalin than ordinary sweet almonds, although concentrations vary substantially among varieties and growing regions. The plant stores the glycoside and the enzymes that activate it separately, a defence system that keeps the toxin contained until the seed is damaged.

Amygdalin was isolated from bitter almonds in 1830. In the twentieth century, it was marketed as “laetrile” and misleadingly promoted as vitamin B17, even though it is neither a vitamin nor an effective cancer treatment. The alternatives listed here are toxins from other plants and are not the compound responsible for bitter-almond cyanide risk.