Stereochemical and pharmacological differences between naturally occurring p-synephrine and synthetic p-synephrine

Abstract

p-Synephrine, the primary protoalkaloid in Citrus aurantium (bitter orange) and some other Citrus species, exists in nature in the l- or [R-(-)]-enantiomeric form, whereas synthetic p-synephrine is a racemic mixture of the l- and d-enantiomeric forms. Based on receptor binding, the synthetic form is believed to exert approximately half the pharmacological activity of the naturally occurring protoalkaloid. This difference occurs because the d- or [S-(+)]-form provides little or no binding to adrenergic receptors in contrast to the l-form. Receptor binding studies also provide an explanation for the differences in pharmacological effects between the isomers p-synephrine and m-synephrine. © 2011 Elsevier Ltd.