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The crystal structures of ephedrine-N-benzyloxycarbonyl-L-leucine (1 ) (P2,2,2,, a = 14.067, b = 29.982, c = 5.737 A) and ephedrine-N-acetyl-L-valine monohydrate (2) (P2,2,2,, a = 13.501, b = 19.1 73, c = 7.694 A) are reported and the conformations of the ephedrine moieties are compared with those in other structures. Charge-charge interactions, hydrogen bonding, and specific phenyl-phenyl interactions play a part in these stereospecific crystallisations. ( -)-Ephedrine is an alkaloid produced by plants of the Ephedra family which have been used for over 5 OOO years as a treatment for bronchial asthma, hay fever, and other allergies.' The naturally occurring compound has the S-configuration at the a-carbon [C(2)] and the R-configuration at the b-carbon [C( l)],and is about 40 times more biologically active than the other isomers. As an optically active organic base, it has been widely used as a chemical resolving and is frequently able preferentially to co-crystallise with one component of a racemic acid solution. In one study: D( -)-ephedrine was used to complex with and resolve a series of N-benzyloxycarbonyl (N-Cbz) derivatives of P-methyl-D-aspartate, D-leucine, Dmethionine, L-phenylaline, L-valine, and L-isoleucine. Our previous crystallographic studies 5*6 of Pasteur's method to resolve amino acids using strychnine and brucine suggested that the distinctive sheet-like packing arrangement of the cation to

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