Barbiturate/diaminopyridine

Considering tridentate sites, 2,6-diaminopyridine and uracil are complementary single site groups (see Sections 9.4.2 and 9.4.3 below). On the other hand barbituric acid (BA) and 2,4,6-triaminopyrimidine (TAP) or -triazine (TAT) are Janus molecules containing two identical recognition sites while 168 is plerotopic by virtue of its two complementary sites (see Section 9.4.4). 

Often designated briefly as Hamilton receptor , this barbiturate receptor niche (Fig. 6.12) consists of an isophthaloyl spacer flanked by two acylated 2,6-diaminopyridine moieties. Macrocyclisation with a rigid diphenylmethane unit generates a non-collapsing host cavity suitable for selective complexation of barbiturate guest molecules via formation of six hydrogen bonds. 

FIGURE 31. Binding of a barbiturate by an immobilized diaminopyridine derivative. Reprinted with permission from Reference 244. Copyright (1994) American Chemical Society... 

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