We now report the preparation of 'stereo-selective adsorbents' suitable for application to the allocation of configurations to stereoisomers. The adsorbent is prepared in the presence of a suitable reference compound of known configuration. After treatment, such a 'stereoselective adsorbent' exhibits higher adsorptive power for isomers of configuration related to the reference substance than for their respective stereoisomers, provided their structures are not too dissimilar from that of the reference compound. The following example illustrates the principle of the method and demonstrates the degree of con-figurational selectivity of suitable 'stereoselective adsorbents'. Silica, gel was prepared in the presence of quinine, partialiy dried, partially extracted with methanol, dried, powdered and then extracted with methanol until no more alkaloid was released from the powder. This process yields an adsorbent the surface of which appears to contain molecular imprints of the desired configuration. A control gel prepared similarly, but in the absence of quinine, adsorbs this alkaloid from solution less readily than does the 'stereo-selective adsorbent' ; the latter adsorbs quinine much more readily than its stereoisomer, quin-idine (see Fig. 1). This adsorbent may now be used to distinguish between the configuration of stereoisomers of structure not too dissimilar from that of quinine ; for example, cinchon-idine (configurationally related to quinine) is adsorbed more readily than its stereoisomer, cinchonine (configurationally related to quin-idine) (see Fig. 1).It is possible to obtain reproducible results with a given batch of adsorbent; batch-to-batch variation is not great if the conditions of preparation are strictly controlled (see Table 1). Even when batch variation occurred, the relative adsorptive power for the different isomers remained of the same order. In Table 1, the results of the adsorption of isomers in a typical experiment using a 'quinidine-selective adsorbent' are also recorded. As one would expect, this adsorbent shows a greater selectivity for quinidine and cinchonine than for their respective stereoisomers, quinine and cinchonidine.Table l. ADSORPTION OF STEREOISOMERS ON A QUININE-SELEOHVE ADSORBENT AND A QUINIDINE-SELECTIVE ADSORBENT 1 gm. of adsorbent used to 10 gm. of solution (25 0 x 10- moleper kgm. in 5 per cent acetic acid) Adsorbent Batch No. Uptake expressed as moles x 105/kgm. of adsorbent of Quinine Quinidine Cinchonine Cinchon-idineQuinine-selective adsorbent 1 217 160 163 207 2 210 161 167 200Quinidine-selective adsorbent 1 194 224 218 190 1 196 228 216 193Table 2. ADSORPTION OF STEREOISOMERS ON A QUININE-SELECTIVE ADSORBENT 1 gm. of adsorbent used to 10 gm. of solution (50 0 x 10-mole per kgm. in 5 per cent acetic acid)Uptake expressed as M x 105/kgm. of adsorbent of: 9-Deoxy- 9-Deoxy- 9-Deoxy- 9-Deoxy- 9-Deoxy- 9-Deoxy-quinine quinidine cinchonine cinchonidine quitenine quitenidine 392 368 358 384 252 225The uptake of various isomeric pairs of quinine-type compounds on a 'quinine-selective adsorbent' is recorded in Table 2. Compounds of like configuration to quinine (9-deoxyquinine, 9-deoxycinchonidine and 9-deoxyquitenine) are adsorbed to a greater extent than their corresponding stereoisomers (9-deoxyquinidine, 9-deoxycinchonine and 9-deoxy quitenidine), although, the degree of discrimination by this adsorbent for one isomer of each pair is less pronounced than for those isomers recorded in Table 1. However, the discrimination is sufficient to permit assignment of configuration to be made from the results. Fig. 1. Adsorption of various stereoisomers on quinine-selective adsorbents and control adsorbents (mean results for numerous batches)Efficient 'stereo-selective adsorbents' have been obtained for optical and geometrical isomers of various classes of compounds, for example, alkaloids, morphinans; details of the preparation of these adsorbents and their application in configurational analysis will be given elsewhere. Investigation of such 'selective adsorbents' as models for biological receptor surfaces3 is in progress, and their use in chromatographic separations is being explored. We are grateful to Prof. H. Veldstra, Combined Quinine Works, Amsterdam, for kindly supplying certain of the isomers used in this investigation.