Dendritic, 1,1 '-binaphthalene-derived cleft-type receptors (Dendroclefts)for the molecular recognition of pyranosides

Two series of optically active, cleft-type dendritic receptors (dendrocleft s) for carbohydrate recognition were prepared by attaching Frechet-type den drons via ethynediyl linkers to a core consisting of one or two 1,1'binapht halene-2,2'-diyl phosphate moieties. Sugar substrates were expected to bind via bidentate ionic H-bonding of two OH groups to the phosphodiester core and, additionally, to undergo van der Waals and CPI a interactions with the aromatic rings of the surrounding dendritic wedges. The synthesis of the d endritic receptors G-1-(S)-1 G-2-(S)-2, and G-3-(S)-3 (Fig. 1; G-x=dendriti c generation) with a single binaphthalene core started from 3,3'-diethynyla ted MOM-protected (MOM = methoxymethyl)1,1'-binaphthalene-2,2'-diol (S)-13 to which the Frechet-type dendrons of generations 1-3 were attached via Son ogashira cross-coupling (Scheme 3). MOM-Ether deprotection followed by phos phodiester formation and ion exchange provided the targeted receptors. By a similar route, receptor G-1-(S)-23 with dendritic wedges capped with oligo ether groups was obtained (Scheme 4). In receptor G-1-(S)-26, the ethynediy l linker was omitted, and, in its synthesis, the dendritic wedges were atta ched to MOM-protected 3,3'-diiodo-1,1'-binaphthalene-2,2'-diol by Suzuki cr oss-coupling (Scheme 5). The synthesis of the dendritic receptors G-2-(S,S) -42 and G-1-(S,S)-43 with two binaphthalene moieties at the core (Fig. 3) s tarted from diethynylated (S,S)-39 and (S,S)33, which contain two MOM-prote cted 1,1'-binaphthalene-2,2'-diol moieties bridged by p-phenylene or buta-1 ,3-diynediyl linkers. respectively, and was completed by attachment of the dendritic wedges by Sonogashira coupling, MOM-ether deprotection, phosphodi ester formation, and ion exchange (Schemes 9 and IO). By an alternative rou te, the C-frame of receptor G-2-(S,S)-41 was prepared by coupling the dendr on to dialkynylated 1,1'-binaphthalene (S)44, followed by oxidative Glaser- Hay coupling (Scheme 8). For control studies, the non-dendritic reference r eceptors (S)-4 and (S)-5 (Fig. I) with one and (S,S)31 and (S,S)-32 (Fig. 2 ) with two 1,1 '-binaphthalene-2,2'diyl phosphate moieties were also prepar ed. LH-NMR Complexation studies with the dendritic receptors containing one binaphthalene core and octyl glycosides 53-55 in CD3CN and CDCl3, (Tables 2 - 4) revealed that ionic H-bonding between the phosphodiester core in the dendritic receptors and the sugar OH groups provides the major driving for ce for stoichiometric 1:1 host-guest association. A smaller, yet significan t contribution to the binding free enthalpy was also provided by interactio ns between the sugar guests and the dendritic wedges. Binding selectivity w as weak in all cases, and only small changes in association strength were o bserved as a function of dendritic generation. In studies with the dendriti c receptors, which contain two binaphthalene moieties at the core, higher-o rder complex stoichiometries prevented the determination of quantitative bi nding data. As a result of unfavorable steric interactions between the dend ritic wedges, these flexible receptor systems apparently avoid adopting the 'syn'-conformation with convergent phosphodiester sites that is required f or efficient 1:1 host-guest complexation.