2-hydroxypropyl 4-nitrophenyl phosphate

Fig. 40 (top) Cationic portion of bifunctional zinc complexes and relative second-order rate constant values and (bottom) intramolecular transesterification reaction of 2-hydroxypropyl 4-nitrophenyl phosphate (HPNP). 

The 2-hydroxypropyl 4-nitrophenyl phosphate (HPNP) transesterification reactivity (Fig. 40, bottom) of binuclear zinc complexes of the dianionic ICIMP and trianionic BCIMP ligands (Fig. 62) have been compared.245 Notably, both of these ligands contain imidazole and carboxylate donors akin to protein-derived residues that are found as ligands to the zinc centers in phosphate-ester-hydrolyzing enzymes such as phosphotriesterase. The initial rate for HPNP transesterification promoted by [(ICIMP)Zn2(Ph2Ac)]C104 in 50% acetonitrile-water solution (tris buffer) was determined to be five times faster than the reaction promoted by [(BCIMP)Zn2(Ph2Ac)]. 

This approach was recently extended to target the cleavage of RNA model compounds." A polypeptide that adopts a characteristic helix-loop-helrx conformation and accelerates the hydrolysis of the RNA model substrate 2-hydroxypropyl 4-nitrophenyl phosphate (HPNP) by about 2 orders of magnitude was used in this investigation. Two histidine and two arginine units in this peptide were believed to be responsible for catalytic activity. Analogs of... 

In spite of the above mentioned Co(EII) compounds, kinetically labile metal complexes may provide fast product/substrate exchange and some of these systems show real catalytic activity. In native dinuclear phosphatases Mg(II), Mn(II), Fe(II/III), or Zn(II) ions are present in the active centers. Although the aqua complexes of the weakest Lewis acids, Mg(H) and Mn(II), show measurable acceleration of e.g. the transesterification of 2-hydroxypropyl p-nitrophenyl phosphate HPNP, [Mn(II)] = 0.004 M, kobs/ uncat = 73 at pH 7 and 310 K, [38] or the hydrolysis of S -uridyluridine (UpU) [39], only a few structural [40] but no functional phosphatase-mimicking dinuclear complexes have been reported with these metal ions. 

Many artificial systems have been designed recently to imitate the function and behaviour of native enzymes - biomimetic chemistry [27]. Among them, calixarene-based receptors bearing one, two or three Zn(II) complexes on the upper rim were prepared as a model for phosphoesterases [28-31]. Dinuclear receptor 25 was reported to enhance the rate of transesterification of the RNA model substrate 2-hydroxypropyl-p-nitrophenyl phosphate more than 20,000 times compared with the non-catalysed reaction. The complexation mode for the phosphate anion can be described as cascade complexation where the anion is coordinated within the cavity formed by two zinc cations. 

The kinetics and cleavage products of 2-hydroxypropyl p-nitrophenyl phosphate (71) have been investigated in methanol containing a di-Zn(II) complex of bis-l,3-A i,A i -(l,5,9 triazacyclododecyl)propane (72) (Scheme 14). " Time-dependent H-NMR spectra of the reaction mixture at... 

Artificial phosphodiesterases that combine a guanidinium unit with a general base connected by a m-xylylene linker catalyse the transesterification of the RNA model compound 2-hydroxypropyl /t-nitrophenyl phosphate (Scheme 20 e.g., B = imidazole). The bifunctional catalysts showed varying extents of cooperation between catalytic units, and a rate enhancement of 4 x 10" was seen in the most favourable case. ... 

The bimetallic complex 2—Zu2 is a highly efficient turnover catalyst of the transesterification of the RNA model compound 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) (Eq. 26.1). A 23,000-fold rate enhancement is observed in the presence of 2—Zn2 (0.48 mM catalyst concentration, 50 % MeCN-20 mM aqueous buffer, pH 7,25 °C) [16]. The two metal ions in 2—Zn2 efficiently cooperate both in... 

Another outstanding study on the usage of an effective calixarene derivative as a biomimetic catalyst for the cleavage of the RNA model compound, 2-hydroxypropyl p-nitrophenyl phosphate was reported by Baldini et al. [35]. They prepared four calix[4]arene derivatives substituted with two to four guadinium moieties at the upper rim of calixarenes, and investigated their catalytic affinities in the cleavage of the RNA model compound 2-hydroxypropyl p-nitrophenyl phosphate in water (see Figs. 27.17 and 27.18). They found that the... 

Fig. 27.18 Cleavage of the RNA model compound 2-hydroxypropyl p-nitrophenyl phosphate in the presence of calixarene-based pseudo-biocatalyst [35]...

A DFT study of the cleavage of a DNA model, p-nitrophenyl methyl phosphate (47), and two RNA models, p-nitrophenyl 2-hydroxypropyl phosphate (48) and phenyl 2-hydroxypropyl phosphate (48 H for NO2), promoted by the dinuclear Zn(II) complex of l,3-bis(l,5,9-triazacyclododec-l-yl)propane formulated with a bridging methoxide (49), was undertaken to determine possible mechanisms for the tfansesterification processes that are consistent with experimental data. The initial substrate-bound state of... 

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