Four new ADDA receptors for DAAD·ADDA heterodimer formation by quadruple hydrogen bonds have been prepared. Their solubility has been improved by substitution with polyethylene glycol or branched alkyl chains. Three ADDA urea structures 8, 9, and 10 possess stabilizing intramolecular hydrogen bonds, in contrast to a related amide 7. The association constants Kass span several orders of magnitudes, with pyrimidinones 8 and 9 showing Kass values above 104 M–1.