Uracil-2,6-diaminopyridine

The DNA base pairs guanine (G), cytosine (C), adenine (A) and thymine (T). The uracil-2,6-diaminopyridine pair can also form three hydrogen bonds but has a much lower association constant than G-C. 

Jorgensen WL, Pranata J. Importance of secondary interactions in triply hydrogen bonded complexes guanine-c34osine vs uracil-2,6-diaminopyridine. J Am Chem Soc 1990 112 2008-2010. 

Complementary triple hydrogen-bond formation involving transition metal complexes has been little studied. Mingos et al. [68] have investigated the cocrystallisation of platinum(II) complexes of the uracil derivative orotic acid (2,6-dioxo-l,2,3,6-tetrahydropyrimidine-4-carboxylic acid), which generally coordinates as the dianion, and 2,6-diaminopyridine (2,6-dap), in which complementary A-D-A---D-A-D triple hydrogen bonds are formed between the orotate... 

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). 

This was realized with derivatives of the complementary heterocyclic groups 2,6-diaminopyridine P and uracil U bearing long aliphatic chains [9.150]. Whereas the pure compounds did not show liquid crystalline behaviour, 1 1 mixtures gave a metastable mesophase of columnar hexagonal type. The existence of the latter was attributed to the formation of a mesomorphic supermolecule 173 via association of the complementary components. 

Lehn s group have designed an extremely novel helix-forming system based on the pairwise association of mutually complementary hydrogen-bonded units.94 The complementary hydrogen-bonded units chosen were derivatives of 2,6-diaminopyridine (P) and uracil (U), which interact readily to form a hydrogen-bonded PU dimer (10.128). 

The most commonly used ADA modules contain the pyrimidine-2,4-dione nucleus. Not surprisingly, N-alkylation of thymine or uracil with an alkyl halide provides a simple, one-step method of functionalizing this module. Other ADA units include simple imides (e.g., 10), heterocycle 13, which was used by Kelly in a bisubstrate reaction template [17], and the anthyridinone or anthyridan units in 15 and 18, respectively. The latter modules are synthesized by double Friedlander condensation of 2,6-diaminopyridine-3,5-dicarboxal-... 

Indeed when an uracil component Ui is combined with the complementary LP2 unit in 2 1 ratio a mesophase is obtained its occurrence may be attributed to the formation of mixed 2 1 supermolecules such as 5, which forms a mesophase having a columnar structure of rectangular section and a very wide domain of liquid crystallinity (from <20 to 111-116°C, for R = C12H25, m = C11H22, n = C16H32 in 5). Similar observations were made for the 2 1 combination of a diaminopyridine unit Pi with the complementary LU2 component [21],... 

A complementary hydrogen-bonded pair between N,N -2,6-pyridinediylbi-sacetoamide and uracil has the potential to develop hydrogen-bonded supramolecular polymers. Two homoditopic monomers 1 and 2 were synthesized 2 was composed of two diaminopyridines connected by a tartrate linker, and two uracil derivatives were used in 1. The complementary triple hydrogen bonds facilitated the polymerization between 1 and 2 to produce liquid crystalline hydrogen-bonded supramolecular polymers. 

Fig. 36 Hydrogen-bonding interaction between polyphenylenevinylene (56) and fuller-ene (57) derivatives functionalized with uracil and diaminopyridine units, respectively...

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