The preparation of L-("R")-coniine by the reduction of β-coniceine (L-propenylpiperidine) by Löffler and Friedrich provides means for converting conhydrine to L-("R")-coniine. Hess and Eichel reported, incorrectly, that pelletierine was the aldehyde (β-2-piperidyl-propaldehyde) corresponding to coniine, and yielded "rac-"coniine when its hydrazone was heated with sodium ethoxide in ethanol at 156–170 °C. According to these authors, D-("S")-coniine is rendered almost optically inactive when heated with barium hydroxide and alcohol at 180–230 °C. Leithe has shown by observation of the optical rotation of (+)-pipecolic acid (piperidine-2-carboxylic acid) and some of its derivatives under varying conditions, that it must belong to the D-series of amino acids.