Influence of Hydrogen Bonding in Competition with Lattice Interactions on Carbonyl Coordination at Phosphorus. Implications for Phosphoryl Transfer Activated States¹

A series of phosphorus compounds containing carboxyl groups that serve as mimics for amino acid residues was synthesized. The series was composed of the phosphonium salts 1A, 1B, and 2, the anionic phosphines 3A and 3B, and the anionic phosphine oxide 4. X-ray structural analysis revealed that P−O coordination occurred in the presence of extensive hydrogen bonding and led to pseudo or regular trigonal bipyramidal geometries. 31P chemical shifts indicated retention of the basic coordination geometries in solution. The two forms observed for 1 and 3 revealed the influence of hydrogen bonding on the P−O donor interactions while 2 and 4 showed the influence of molecular packing effects in competition with hydrogen bonding interactions. The results suggest that phosphoryl transfer enzyme mechanisms should benefit by taking into account P−O donor interactions by residues at active sites that can be manipulated by hydrogen bonding and molecular packing effects in enhancing nucleophilic attack at phosphorus centers.本研究合成了一系列含羧基的磷系化合物，用作氨基酸残基的模拟物。该系列化合物包括鏻盐(phosphonium salt)1A、1B与2，阴离子膦(anionic phosphines)3A、3B以及阴离子氧化膦(anionic phosphine oxide)4。X射线结构分析显示，在存在大量氢键的条件下会发生P-O配位作用，并形成假三角双锥或正三角双锥的空间构型。31P核磁共振化学位移结果表明，此类化合物在溶液中仍保持其基本配位几何构型。针对化合物1与3观察到的两种存在形式，揭示了氢键对P-O给体相互作用的影响；而化合物2与4则展现出与氢键作用相互竞争的分子堆积效应的影响。本研究结果表明，在探究磷酰基转移酶(phosphoryl transfer enzyme)的催化机制时，应考虑活性位点残基所参与的P-O给体相互作用；这类相互作用可通过氢键与分子堆积效应进行调控，从而增强亲核试剂对磷中心的进攻。