Hydrolysis of oxaliplatin-evaluation of the acid dissociation constant for the oxalato monodentate complex

Alkaline hydrolysis of the platinum anticancer drug oxaliplatin gives the oxalato monodentate complex and the dihydrated oxaliplatin complex in two consecutive steps. The acid dissociation constant for the oxalato monodentate intermediate was determined by a kinetic approach. The pK(a) value was estimated as 7.23. The monodentate intermediate is assumed to rapidly react with endogenous compounds, resulting in a continuous conversion of oxaliplatin via the monodentate form.     

Alkaline hydrolysis of cladribine

The kinetics of hydrolysis of 2-chloro-2'-deoxyadenosine (cladribine) was studied at various sodium hydroxide concentrations and temperatures. HPLC analysis of reaction mixtures showed that the main products were 2'-deoxyisoguanosine and 2'-deoxyguanosine. The first one was the result of the hydroxyl anion attack, whereas the presence of the other nucleoside has evidenced the existence of hitherto undescribed rearrangement reaction in purine derivatives.     

Alkaline hydrolysis of 1,3-dimethylphenobarbital.

The reaction of 1,3-dimethylphenobarbital (I) with 0.02-0.32 M KOH in aqueous methanol was studied. The barbiturate ring cleaved reversibly at the 1,6-position, forming a malonuric acid which was stable to further hydrolysis but which could readily recyclize to I. N,N-Dimethylethylphenylmalondiamide arose from decarboxylation of the carbamic acid formed by a 1,2-ring opening; this irreversible decarboxylation determined the diamide as the only final reaction product. The malonuric acid, which could be isolated in solid form, appeared as N-methyl-2-phenylbutyramide (GLC) following thermal decarboxylation and degradation of the acid. The I disappearance rate was biphasic, and the kinetics were consistent with the described reaction. The individual rate constants and the equilibrium constant for the reaction between I, the malonuric acid, and hydroxide were determined.     

Base-catalyzed hydrolysis of 4-hydroperoxycyclophosphamide: evidence for iminocyclophosphamide as an intermediate

cis-4-Hydroperoxycyclophosphamide (5) undergoes facile reaction with aqueous phosphate or Tris buffers at pH 7-8 and 30 degrees C. The kinetics of 5 are complex, and the trans-4-hydroperoxy isomer 6 is produced and subsequently disappears over the course of the reaction. Addition of hydrogen peroxide to the reaction mixture retards the disappearance rate of 5 and increases the amount of 6 generated. Rate constants for the reversible disappearance of 5 and appearance of 6 and 4-hydroxycyclophosphamide (2) have been determined by nonlinear least-squares methods. The reaction is catalyzed by hydroxide ion, Tris free base, and HPO4 2-, with catalytic constants of 0.032 min-1 (pH 8.0), 0.052, and 0.115 M-1 min-1, respectively. The major product in the presence of Tris is the oxazolidine 8b arising from the addition of Tris to aldophosphamide, not 2 as assumed previously. These results are consistent with a mechanism involving general-base-catalyzed elimination to produce iminocyclophosphamide 7 as a transient intermediate; the imine can react with the hydrogen peroxide evolved in the reaction to give 5 and 6, with water to give 2, or, in general, by addition of a nucleophile to C-4. The significance of these findings with respect to other 4-substituted cyclophosphamides is discussed.     

Alkaline hydrolysis of methyl, ethyl and n-propyl 4-hydroxybenzoate esters in the liquid and frozen states

The alkaline hydrolysis of the methyl, ethyl and n-propyl esters of 4-hydroxybenzoic acid was studied in the liquid and frozen states in sodium hydroxide solutions. The temperature range was −26 to 60°C. Significant acceleration of the reaction rate was evident in the frozen state compared with rates found at liquid state temperatures. The maximum reaction rate in the frozen state occurred in the temperature range −12 to −10°C. Methyl 4-hydroxybenzoate showed more than a 20-fold increased rate constant from 7.17 × 10⁻⁶ s⁻¹ at 30°C to 1.53 × 10⁻⁴ s⁻¹ at −9°C in a 1.00 × 10⁻² M solution of sodium hydroxide. Rate constants in the liquid and frozen states followed pseudo first-order kinetics over 2–4 half-lives of reaction. Data were fitted to a theoretical model describing the reaction rate in the frozen state as dependent upon the increased concentration of solutes in liquid vesicles in the frozen state and the predicted reduction in the reaction rate constant with temperature decrease. Although the data exhibited similar trends to that predicted by the model, there was frequently a 50% difference in the rates observed compared with those predicted. This study has clearly demonstrated that there is a significantly increased rate of hydrolysis of these esters in the frozen state. This is a further indication that it cannot be assumed that drugs stored in solution will necessarily be stabilized, or their stability enhanced, on freezing. Storage under refrigeration conditions (4–8°C) results in enhanced shelf-lives compared with deep-freeze storage at −20°C under the conditions of this study.     

Acid-catalyzed hydrolysis of BMS-582664: degradation product identification and mechanism elucidation

BMS-582664 is an investigational drug intended for cancer treatment through oral administration. The preformulation studies revealed two unexpected degradation products under acidic conditions by reversed-phase high-performance liquid chromatography with ultraviolet detection. Additional liquid chromatography-mass spectrometry results suggested that these were cleavage (hydrolysis) products of a diaryl ether. To further understand the degradation mechanism, the reaction was carried out in (18) O-labeled water. The (18) O was found to be incorporated in only one of the two hydrolysis products. The results suggest that the corresponding α carbon in the heterocycle was unusually eletrophilic in acidic conditions probably because of the protonation of the neighboring nitrogen. This led to the selective attack by water and the consequent hydrolysis products. The study provides a new example of hydrolytic degradation of pharmaceutical compounds, and the reaction center is an aromatic heterocyclic carbon with an aryloxy substitution.     

方格星虫多肽的结构分析及体外抗氧化活性

目的 以方格星虫为原料,酶解制备水溶性多肽并考察其抗氧化活性,探究其结构-活性关系。方法 利用5种蛋白酶酶解新鲜方格星虫,并结合超滤方法得到高分子量(>50kDa)、中分子量(5～50 kDa)和低分子量(＜5kDa)的酶解肽段;利用氨基酸自动分析仪测定方格星虫酶解肽的氨基酸组成。综合考察多肽对1,1-二苯基-2-苦基肼(DPPH.)自由基、羟基自由(.OH)、超氧阴离子自由基( O-2.)的清除能力以及还原力效果,评价方格星虫多肽抗氧化活性;利用高效液相色谱-串联质谱方法鉴定小分子肽的氨基酸组成和序列结构。结果 胰蛋白酶水解方格星虫4h得到的酶解液蛋白含量最高,并在酶解液中检测确定了17种氨基酸,其中精氨酸含量最高13.65%。高中低三组肽段中,低分子量肽段的抗氧化活性优于其他：对DPPH 自由基和羟自由基清除能力大小顺序为低分子量>高分子量>中分子量、对超氧阴离子清除能力大小顺序为低分子量>高分子量≈ 中分子量、还原能力强弱顺序为高分子量>低分子量 > 中分子量。经高效液相色谱-串联质谱联鉴定了GFAGDDAPR、GLGGLSPEK 、LDLAGR和VTKEIPR 4个肽段。结论 低分子量的方格星虫酶解多肽具有较好的抗氧化活性,有潜力用作生物医药或化妆品工业的原料。     

Alkaline hydrolysis of oligomers of tartrate esters: effect of a neighboring carboxyl on the reactivity of ester groups.

The importance and the effect of neighboring groups on the hydrolysis of polymeric esters were demonstrated. Several oligomers of poly(butylene tartrate) were synthesized, and their kinetic behavior was studied under alkaline conditions. The oligomers and their degradation products were monitored by HPLC and identified by fast atom bombardment mass spectrometry. The rates of hydrolysis measured at pH 5-8 and at 75 degrees C indicate that the degradation of the oligomers obeyed pseudo-first-order kinetics. The rate of hydrolysis among the homologous series of oligomers increased as the molecular weight increased. However, the increase in hydrolysis rate was not proportional to the number of ester linkages in the oligomers. This deviation was explained on the basis of electrostatic repulsion of the neighboring carboxylate group toward the hydroxide ion. The calculations revealed that the electrostatic effect was so great that the ester linkage adjacent to the carboxylate anion did not contribute to the overall rate of hydrolysis. The technique presented here can be extended to any multifunctional-group compound that has repeat units and can undergo a specific reaction that can be accurately measured.     

关于对《中国药典》2020年版盐酸普鲁卡因水解鉴别试验的修订建议

目的：针对《中国药典》2020年版盐酸普鲁卡因水解鉴别试验中水解温度、时间及盐酸浓度、用量等未提供参考数据,影响实验快速准确进行和实验现象出现,提出改进方法,为《中国药典》2020年版盐酸普鲁卡因水解鉴别试验的修订提出建议。方法：分别考察水解温度及盐酸（36%）加入量、盐酸浓度（36.0%、10.0%、5.0%、2.5%、0.625%）及用量对实验现象的影响,明确水解温度及时间、盐酸浓度及用量参考值。结果：不同温度下水浴加热,随着水浴温度的升高,热至油状物消失的时间逐渐缩短;以36%盐酸酸化,至出现白色絮状沉淀,消耗盐酸的量为0.1～0.2mL,即2～4滴;继续加盐酸0.05mL即1滴后白色絮状沉淀消失,溶液澄清。采用电热套加热（平均加热温度为275??℃）,各组加热至油状物消失的时间较为接近,约为10min。随着盐酸浓度的降低,滴加盐酸至白色沉淀现象出现所消耗盐酸的量逐渐增加,继续滴加盐酸至溶液澄清消耗盐酸的量也逐渐增加。但即使盐酸浓度稀释至0.625%,滴加盐酸也会出现白色絮状沉淀现象。结论：从操作便捷省心省力、既保证加热水解完全又避免溶液蒸干,可考虑用水浴。综合考虑白色絮状沉淀（对氨基苯甲酸）的生成,同时避免滴加盐酸过量致使沉淀消失,可以10%盐酸进行酸化。