Some of these compounds are toxins such as the alkaloid coniine from hemlock. Currently, Coniine, and many other alkaloids, can be synthesized stereoselectively. Coniine, the main poison in hemlock species, can be absorbed through the skin. The biosynthesis of coniine is still being investigated, much of the pathway has been elucidated. Poison hemlock ("Conium maculatum") contains highly toxic amounts of coniine. Oxygen-free alkaloids, such as nicotine or coniine, are typically volatile, colorless, oily liquids. This is then reduced using NADPH dependent y-coniceine reductase to form coniine. However, this molecule is transformed into coniine later during the fruit development. Coniine also has significant toxic effects on the kidneys. In this way, starting from (S)-alcohol an (S)-enantiomer of Coniine is obtained and vice-versa. Coniine gives no coloration with sulfuric or nitric acid. Coniine dissolves in carbon disulfide, forming a complex thiocarbamate. Coniine has a chemical structure and pharmacological properties similar to that of nicotine. In high enough concentrations, coniine can be dangerous to humans and livestock. Coniine eventually became the first of the alkaloids to be artificially synthesised.