D-propylhexedrine is an optical isomer of propylhexedrine, a vasoconstrictor stimulating α-adrenergic receptors of the sympathetic nervous system. D-propylhexedrine is proposed to be less potent isomer, it is is less pressor and less excitatory on the central nervous system than is the L-isomer.

Betonicine (trans-2-carboxy-4-hydroxy-1,1,-dimethylpyrrolidinium hydroxide, inner salt) and its cis isomer, turicine, are naturally occurring substituted pyrrolidines. Betonicine was used as an analgesic 1000 years ago and is still available commercially from herbalists today. Betonicine has been isolated from Achillea millefolium L. (Compositae) and probably from A. atrata L. (Compositae); it is an alkaloid. Proline betaine and Betonicine were identified as metabolically inert cell protectants against extremes in osmolarity and growth temperatures.