Hydrolytic Stability of Aqueous Solutions of Salicin
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Pharmaceutical Chemistry Journal, Vol. 54, No. 8, November, 2020 (Russian Original Vol. 54, No. 8, August, 2020)
HYDROLYTIC STABILITY OF AQUEOUS SOLUTIONS OF SALICIN S. V. Nekhoroshev,1,* A. V. Nekhorosheva,1 A. B. Sabutova,2 E. Kh. Botirov,3 A. A. Drenin,3 G. B. Slepchenko,4 and N. V. Gornikov3 Translated from Khimiko-Farmatsevticheskii Zhurnal, Vol. 54, No. 8, pp. 58 – 61, August, 2020.
Original article submitted May 11, 2020. The kinetics of salicin acid hydrolysis in aqueous solutions were studied. The salicin content in the reaction mixtures was determined by HPLC with UV detection. The salicin hydrolysis rate depended more on the solution acidity than on the temperature. The dependences of the salicin hydrolysis rate constant on temperature and solution acidity were established. Salicin was most reactive in aqueous solutions at 90ºC and pH < 1.0. Salicin preparations could be stored for more than one year without noticeable decomposition at room temperature and pH > 2.0 Keywords: salicin, hydrolysis, kinetics, glycoside, storage.
Until now, the kinetics of salicin hydrolysis in aqueous solutions have not been studied and the safety limits for this glycoside under processing and storage conditions of salicin preparations in aqueous solutions have not been defined despite salicin being extracted from the plant raw material most often by H2O or its mixture with EtOH [1]. Therefore, the goal of the present work was to study the effects of temperature and pH on the hydrolysis rate of salicin in dilute aqueous solutions and to evaluate its hydrolytic stability in waterbased preparations.
Salicin [D-(–)-salicin, 2-(hydroxymethyl)phenyl-b-Dglucopyranoside] is a natural compound that determines the biological activity of preparations prepared from various vegetative parts of plants in the family Salicaceae [1]. Salicin was isolated from the plant raw material already in the XIXth century and was widely used as a medicine before the appearance on the market of synthetic aspirin at the start of the XXth century [2]. Recently, salicin and plant raw material containing it is more and more often used in practice [3, 4]. HPLC with UV detection is successfully used to determine salicin in plant raw material [5]. The physicochemical properties of salicin (1) were studied mainly abroad during the XIXth and XXth centuries. Enzymatic and acid hydrolysis of 1 was observed to form salicylic acid and glucose [6, 7]. Renewed investigations of enzymatic hydrolysis of 1 found that salicyl alcohol (II) formed first during the reaction (Fig. 1) and was further oxidized into salicylaldehyde (III) that was in turn oxidized to salicylic acid (IV) [8]. 1 2 3 4 *
EXPERIMENTAL PART The following reagents were used in the experiments: salicin (CAS 138-52-3) of purity £99% (Biochem Chemopharma); salicyl alcohol (CAS 90-01-7) of purity £99% (Sigma-Aldrich); salicylaldehyde (CAS 90-02-8) of purity £99% (Alfa Aesar); sodium salicylate, chemically pure; HCl, chemically pure; HBr, chemically pure; H2SO4, chemically pure; MeCN (for UHPLC);
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