Investigating a Relationship between the Mutagenicity of Arylboronic Acids and (11)B NMR Chemical Shifts.

The mutagenicity of arylboronic acids has recently become an important area of research because of their potential to be genotoxic impurities in active pharmaceutical ingredients. There is no known mechanism, so currently all structure-activity relationships have been derived using Ames test data. We present preliminary data supporting a hypothesis that the mutagenicity of arylboronic acids is related to the (11)B NMR chemical shift. This could indicate that the mutagenic activity of the arylboronic acids is related to the reactivity of the boron center.

Design, synthesis and binding studies of a novel quadruple ADDA hydrogen-bond array.

The design and synthesis of a novel ADDA hydrogen-bond array is described. The ureidodiimidazole motif (UDIM) 2 engages in interactions with complementary diamidonaphthyridine (DAN) 3 motifs with an association constant K(a) = 825 ± 16 M(-1) in chloroform. (1)H NMR and molecular modelling studies were carried out in order to explain the unexpected behaviour of this new supramolecular motif. These revealed that a combination of effects including; an energetic bias for the folded conformer, subtle differences in shape complementarity between the two components and the potential for self-association of UDIM 2 disfavour higher affinity interactions between the two components.

Conformer-independent ureidoimidazole motifs--tools to probe conformational and tautomeric effects on the molecular recognition of triply hydrogen-bonded heterodimers.

Linear arrays of hydrogen bonds are useful for the reversible assembly of "stimuli-responsive" supramolecular materials. There is thus an ongoing requirement for easy-to-synthesise motifs that are capable of presenting hydrogen-bonding functionality in a predictable manner, such that high-affinity and high-fidelity recognition occurs. The design of linear arrays is made challenging as a consequence of their ability to adopt multiple conformational and tautomeric configurations; with each additional hydrogen-bonding heteroatom added to an array, the available tautomeric and conformational space increases and it can be difficult to anticipate where unproductive conformers/tautomers will arise. This paper describes a detailed study on the complementary ureidoimidazole donor-donor-acceptor (DDA) array (1) and amidoisocytosine donor-acceptor-acceptor (DAA) array (2). A specific feature of 1 is that two degenerate, intramolecular hydrogen-bonded conformations are postulated, both of which present a DDA array that is complementary to appropriate DAA partners. 1D and 2D (1)H NMR spectroscopy, isothermal titration calorimetry, and ab initio structure calculations confirm 1 interacts with 2 (K(a) ≈ 33,000 M(-1) in CDCl(3)) in a conformer-independent fashion driven by enthalpy. Comparison of the binding behaviour of 1 with hexylamidocytosine (4) and amidonaphthyridine (5) provides insight on the role that intramolecular hydrogen-bonding plays in mediating affinity towards DAA partners.

Substituent control over dimerization affinity of triply hydrogen bonded heterodimers.

Linear arrays of hydrogen bonds represent important elements of the supramolecular toolkit for receptor design, assembly of supramolecular polymers, and other well-defined supramolecular structures. It is illustrated that remote substituent effects control dimerization affinity in a predictable manner using a conformer independent ureidoimidazole DDA motif and its amidoisocytosine based AAD partner.