172 DAVID R. EVANS 



linkage was effective, while the same molecule with a 5-membered (planar) 

 ring (cpd. 9) was inert. Compounds 10 and 1 1 point to essentially the same 

 conclusion. 



That the ring oxygen atom itself is not required for stimulation is sug- 

 gested by cpd. 12, myo inositol. Since this molecule is so different 

 from glucose, it was necessary to obtain evidence that it stimulated by 

 combination at the glucose site. Glucose alone and several mixtures of 

 glucose and inositol of varying properties were tested on 120 animals. 

 Responses to the mixtures averaged 88 per cent of the responses to glucose 

 solutions of equivalent concentration, close to the value that would be 

 expected were the compounds strictly additive in their interaction with the 

 receptor. In addition, an axial hydroyl group on the ring ofinositol where the 

 pyranose oxygen atom usually is located did not interfere with stimulation. 



Removal of the C2 oxygen, methylation of it, or replacement with an 

 amino group had little effect on stimulation (cpds. 13-15) ; but switching 

 the hydroxyl group from the equatorial position to axial rendered it 50 

 times less effective (cpd. 16). As mentioned before, glucose and mannose 

 are strictly additive in mixtures. 



Truly appropriate compounds have not yet been obtained to assess the 

 requirement for the C3 hydroxyl group (e.g. 3-deoxy glucose). Methylation 

 (cpd. 17) or transfer to the axial orientation (cpd. 18) render the molecule 

 ineffective, but the former adds on a larger substituent that might sterically 

 hinder the reaction and pure gulose has not been assayed. 



Appropriate tests have not been made of the C4 and C5 substituents, but 

 the latter normally is part of the pyranase ring and has otherwise only a 

 hydrogen substituent. Galactose (C3-OH axial) stimulates (effectiveness 

 relative to glucose = 0.26), but there is no evidence yet that it reacts with 

 the glucose site. 



The Cq carbinol group appears unimportant since it is lacking in inositol 

 and xylose and since relatively large esteratic substituents (cpd. 20) do not 

 interfere. 



In summary, the evidence is consistent with the view that the hydroxyl 

 groups on C3 and C4 alone are responsible for stimulation. They are 

 trans, but in the CI conformation are respectively inclined about 19° above 

 and 19° below the plane of the ring (see Fig. 1). A two point attachment 

 seems incompatible at first with the degree of specificity the receptor 

 exhibits, but the marked interference noted above by substituents other- 

 wise not involved could contribute to that specificity. 



In accordance with the above considerations is the observation that the 

 synthetic mono- and di-isopropylidene glucose derivatives are non- 

 stimulating — the compound Dethier (1955) tested probably was not diace- 

 tone glucose as indicated above in "Materials and Methods". Consequently, 

 his conclusion that furanose forms of glucose can stimulate appears incorrect. 



