Dimeric 1,3-phenyl-linked

Figure 1.19 Tyrosine and phenylalanine residues can undergo oxidation to modify their phenyl side-chain groups. Tyrosine can form covalent dimers that link two side chains together via a radical reaction. Both tyrosine and phenylalanine can be modified by oxidation to add oxygen-containing groups directly to their aromatic ring.

Chapman and Breslow synthesized zinc(II) complexes of monomer and dimers derived from 1,4,7-triazacyclododecane with phenyl 48 and 4,4 -biphenyl linkers 49 (55). They were examined as catalysts for the hydrolysis of 4-nitrophenyl phosphate (NP2 ) and bis(4-nitrophenyl) phosphate (BNP ) in 20% (v/v) DMSO at 55°C. On the basis of the comparison of the pseudo-first-order rate constants, the dinuclear zinc(II) complexes 48 with 1,3-phenyl and 1,4-phenyl linkers are ca. 5 times more efficient than monomer or 49 in the hydrolysis of NP2, leading to the conclusion that the two zinc(II) ions are simultaneously involved in the hydrolysis, as in the enzyme alkaline phosphatase. For the hydrolysis of BNP, a longer dimer 49 is ca. six times more effective than 1,3-phenyl-linked dimer 48 and monomers. 

From an evaluation of the catalytic efficiency of 3-5 using standard catalytic phase-transfer benzylation of 1, it was found that all compounds had the ability to catalyze this phase-transfer benzylation, and in all cases the (S)-isomer of the benzylated imine 2a was formed in excess (Scheme 4.3). The 1,3-phenyl-linked dimeric PTC 4 showed the highest enantioselectivity among the three dimeric PTCs. The order of enantioselectivity of the three PTCs, along with the monomeric PTC M, was as follows 1,3-dimeric PTC 4 > 1,4-dimeric PTC 5 = monomeric PTC M 1,2-dimeric... 

A bell-shaped pH vs rate profile with a maximum rate at pH 7.8 was seen in NP hydrolysis by 1,3-phenyl-linked dimer 48. The phosphomonoester NP " prefers the two zinc(II) ions to be close, and hence two alternative mechanisms as shown in Scheme 11 (a or b) are proposed for the hydrolysis. The loss of catalytic activity at pH > 12 may be accounted for by the formation of a double OH"-bridged zinc(II)... 

Recent studies have been concerned with the photophysical characterization of a series of quinone-substituted, phenyl-linked porphyrin trimers 3-5 suitable for the study of electron transfer within a system of highly-coupled photoactive subunits [18]. For trimer 4, the most elaborate of these models, the distant (distal) porphyrin-to-quinone center-to-center distance is estimated to be 32.0 A (26.8 A edge-to-edge) as extrapolated from X-ray structural data obtained with monomeric and dimeric models the corresponding center-to-center inter-porphyrin distances are estimated to be 12.8 and 25.5 A (5.86 and 19.9 A edge-to-edge) between adjacent and once-removed porphyrin subunits, respectively. 

Sila-procyclidine, (cyclohexyl)phenyl[2-pyrrolidin-l-yl]silanol, may be prepared by hydrolysis of the corresponding methoxysilane (220) and is interesting in that it can form two types of hydrogen-bonded structure depending on whether it is enantiomerically pure or a racemate. In the racemate, the compound forms centrosymmetric dimers of (R)- and (S)-configuration molecules with an 0---N distance of 1.791 A. In the pure (R)-compound, however, the molecules are linked into infinite chains via intermolecular 0-H---N hydrogen bonds (0---N distance 2.792 A) (221), again similar to those in (2-morpholinoethyl)diphenylsilanol shown in Fig. 3. 

The structure of the 1 1 methanol solvate of olanzapine has been reported, where pairs of olanzapine molecules form a centrosymmetric dimer by means of C—H—-7t interactions [66]. The solvent molecule was linked to the drug substance through O—H-N, N—H O, and C—interactions. In a new polymorph of the 1 1 dioxane solvatomorph of (+)-pinoresinol, the structure was stabilized by O—H O hydrogen bonds between the compound and the solvent [67], Two new polymorphs of 2-cyano-3-[4-(/Y,jV-diethylamino)-phenyl]prop-2-enethioamide and its acetonitrile solvatomorph have been characterized [68], Although crystallization of the title compound was conducted out of a number of solvents, only the acetonitrile solvatomorph could be formed. 

Two molecules with comparable geometry in an asymmetric unit were found for 3,4-bis(4-fluorophenyl)-l,2,5-oxadiazole 2-oxide. The bond length of the dipolar N-O bond is 1.107 (7) A <2006AXEo4827>. In the molecule of 5-(6,7-dimethoxy-l,2,3,4-tetrahydroisoquinolin-2-yl)-4-phenyl-l,2,5-oxadiazole Ar-oxide, the six-membered heterocyclic ring has a flattened boat form. Intermolecular C-H- O hydrogen bonds link the molecules into dimers, which may be effective in the stabilization of the crystal structure <2006AXEo3130>. 

Rotaxane 80e can even be dimerized by reaction with l,3,5-tris(4-methyl-phenyl)benzene (105) [42]. Considering the steric crowding, it is remarkable that the resulting wheel-tris[2]rotaxane ([4]rotaxane) 106 is formed in 35% yield (Figure 42). Extension of the strategy of coupling rotaxanes to multifunctional units should enable easy access to amide-linked dendritic rotaxane structures. 

Phenyl- and 2,7-Naphthyl-Linked Dimeric Cinchona-PTCs... 

Cocrystal systems are assembled through the association of individual molecules into fundamental building block units that are known as supramolecular synthons [13]. For example, one such synthon would be formed by hydrogen-bond interactions between a phenyl-carboxylic acid and a phenyl-amide, with the molecules being linked into a dimeric species through 0 H-N and O-H O hydrogen bonds [14], This mode of interaction can be illustrated using the synthon that would result from the dimerization of benzoic acid and benzamide ... 

B3 is a short notation for V..V -diphenyl-1.4-phcnylcncdiaininc. which is known also as phenyl-end-capped-dimer" of the polyaniline chain [26], B3 consists of three phenyl (benzene-like) rings connected by C-N links as shown in Fig. 1. The interest in this molecule was stimulated by its luminescence properties [27] as well as by the potential applications in the field-effect transistors [28],... 

A theoretical study of the chiral recognition of the bis(amino(phenyl)methanol) chromium(O) complexes and chiral discrimination of the dimers of amino(phenyl) methanol linked by HB has been carried out by means of a DFT method, the B3LYP/6-31+G. The results (Fig. 3.24) show that in the chromium complexes, the homochiral one is preferred over the heterochiral one, while the opposite... 

We have pursued such ester hydrolysis by artificial enzymes further. With a cyclodextrin dimer related to 25 we have hydrolyzed an ordinary doubly bound ester, not just the more reactive nitrophenyl esters [116], with catalytic turnovers. Also, with a catalyst consisting of a cyclodextrin linked to a metal ligand carrying a Zn2+ and its bound oxime anion, we saw good catalyzed hydrolysis of bound phenyl esters with what is called burst kinetics (fast acylation, slower deacylation), as is seen with many enzymes [117]. 

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