Morphine, caffeine and nicotine belong to one bitter chemical family
Quinine, caffeine, nicotine, morphine and strychnine all share one feature: at least one nitrogen atom in a natural molecule. Chemists call them alkaloids, a name coined in 1819 because these plant extracts behaved like alkalis. Many taste bitter, and plants probably evolved them to discourage animals from eating their leaves.
People used alkaloid plants long before anyone could name the chemistry. Medicinal plants were known in Mesopotamia around 2000 BC, and Homer's Odyssey describes a drug of forgetfulness that Helen received from an Egyptian queen, thought to contain opium. Hunters tipped arrows with plant poisons such as aconitine and tubocurarine. The scientific story begins in 1804, when Friedrich Sertürner extracted a sleep-inducing principle from opium and named it after Morpheus, the Greek god of dreams; the French scientist Joseph Louis Gay-Lussac gave it the English and French form, morphine.
A rush of discoveries followed. Pierre Joseph Pelletier and Joseph Bienaimé Caventou isolated strychnine in 1818 and quinine in 1820, the same year caffeine was found, with nicotine arriving in 1828 and cocaine in 1860. In 1886 Albert Ladenburg made coniine entirely in the laboratory, the first alkaloid ever synthesised. Naming habits stuck close to the source plant: atropine from Atropa belladonna, strychnine from the strychnine tree, and at least 86 compounds from vinca plants carrying the root vin.
Classifying them is awkward because their structures vary enormously. True alkaloids come from amino acids and hold nitrogen in a ring, like morphine and nicotine. Protoalkaloids such as mescaline and ephedrine have nitrogen outside a ring. Pseudoalkaloids, including caffeine and theobromine, do not come from amino acids at all. Nicotine even straddles two categories because its halves have different chemical origins.
Between 10 and 25 percent of higher plants contain alkaloids, concentrated in leaves, seeds, roots or bark depending on species. Fungi make them too, as do toads and ants. Some animals have evolved to detoxify them, but not all: in the 1950s, up to a quarter of lambs born to sheep grazing corn lily had serious facial defects caused by cyclopamine. The sea supplies some of the most extreme examples, including tetrodotoxin, found in pufferfish and blue-ringed octopuses and roughly 10,000 times more toxic than cyanide.
Source: Alkaloid
