Chemistry for Sustainable Development 27 (2019) 461–467 461 UDC 577.13:582.623.2 DOI: 10.15372/CSD2019166 Phenol Compounds in the Species of Salix L. Genus in the World Flora A. A. PETRUK Central Siberian Botanical Garden, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia E-mail: [email protected] (Received May 17, 2019; revised July 18, 2019) Abstract Review and analysis of the modern data on the content of phenol compounds in the plants of the Salix L. genus were carried out. The works aimed at the search for cheotaxonomic markers and their application in sys- tematics are presented. It is demonstrated that the qualitative composition of phenol compounds is an invariable, stable sign for the taxons of the Salix genus. Phenol glycosides may be used to identify morphologically similar species and hybrid forms. Special attention is paid to the species that have been the subjects of investigations in different countries: S. babylonica L., S. alba L., S. raddeana Laksch. еx Nasarow, S. caprea L. and S. acutifolia Willd. Keywords: Salix L., phenol compounds, flavonoids, phenol glycosides, chemotaxonomy INTRODUCTION authors [4], Bontsevich [13], Khiteva [14], Frolova with co-authors [15]. The Salix L. genus is one of the numerous gen- The Salix genus is represented by three sub- era of Salicaceae Mirb. family, it includes 552 spe- genera: Salix, Vetrix Dumort. and Chamaetia cies of the world flora [1]. The number of species (Dumort.) Nasarow, according to the traditional indicated for Russia and adjacent territories is 158 classification based on the morphological and eco- [2], for the Asian part of Russia – 103 species [3]. logical-geographical characteristics of the repre- There are data on the antipyretic, disinfecting, sentatives of the genus [16, 17]. The systematic astringent activity of osier bark both in folk and position of the species, ecological-morphological in traditional medicine [4, 5]. Research into the characterization are presented according to the lit- hemostatic, diuretic, antimicrobial, antiinflamma- erature and electronic sources [1, 3, 16, 17]. Cycles tory and antitumour activity of the extractive of studies in different countries have been dedi- substances of the plants of Salix genus are car- cated to separate species during the two recent ried out [6–10]. Osier bark is one of the compo- decades: S. babylonica L., S. alba L., S. raddeana nents of antirheumatic and antifebrile medicinal Laksch. ex Nasarow, S. caprea L. and S. acutifolia preparations in many countries [4]. The curative Willd. The data on the pharmacological activity properties of osier are due to the presence of were described in detail in the indicated works. phenol compounds in the raw material [11, 12]. The goal of the present work was to make a The information on the chemical composition of review of research and analysis of modern litera- the species of Salix genus and their pharmaco- ture data on the composition of phenol com- logical activity was published by Zuzuk with co- pounds in the plants of Salix genus, and evalua- © Petruk A. А., 2019 462 A. A. PETRUK Fig. 1. The structural formulas of the main phenol compounds of Salix L. genus: а – salycine, b – naringenin , c – astragaline, d – prunine, e – taxifolin. tion of the possibility to use them as chemotaxo- that total flavonoid content is higher in leaves nomic markers. than in branches and in blossom clusters. It reached its maximum (6.044 %) in May, and min- imum (1.875 %) in July [19]. The compounds iso- PHENOL COMPOUNDS lated from the methanol extract of the leaves of S. babylonica include 7-О-β-D-glucuronid of The structural formulas of the main phenol chrysoeriole, 7-О-β-D-galactopyranoside of lute- compounds present in the plants of the Salix L. olin, 7-О-glucoside of kaempferol, 7-О-galactoside genus are presented in Fig. 1 [18]. of apigenin, 4'-О-glucoside of luteolin, salycine, Salix babylonica trichocarpine, and a new phenol glycoside 2-О-acetyltrichocarpine (benzyl ester of 2-О-β- S. babylonica L. (= S. matsudana Koidz.) is D-glucoside of gentisic acid) [20, 21]. In addition, weeping willow belonging to the Subalbae Koidz. the compounds discovered in the leaves of S. bab- subsection of Salix subgenus. It is a tree up to 15 ylonica for the first time include β-D- m high. The species is widespread in culture al- glucopyranuronide of apigenine, 7-О-β-О- most in all regions with moderate warmth over glucopyranuronide of luteolin and 7-О-β-D- the globe. The origin is in arid and semi-arid re- glucopyranuronide of chrysoeriole [22]. Later a gions of Central and Northern China. new flavonoid named matsudon was isolated, Within several recent years, works dealing along with five known flavonoids, such as luteo- with the studies of composition and dynamics of lin, isoquercetin, 7-methoxyflavon, 7-О-glucoside phenol compounds in S. babylonica plants were of luteolin, 4',7-dihydroxyflavon, and two phenol published in China [19–25]. It was established glycosides – leonuriside and piceoside. Their P HENOL COMPOUNDS IN THE SPECIES OF SALIX L. GENUS IN THE WORLD FLORA 463 structures were determined on the basis of ex- In China, several works dealt with this species tensive studies by means of 1D- and 2D-NMR, [28–33]. For example, in 2004 high-performance mass spectrometric analysis and comparison with liquid chromatography (HPLC) was applied to literature data [23]. The content of phenol isolate raddeanalin (7-О-glucopyranoside of dios- compounds in the abscissed leaves of the plants metin) from S. raddeana and identify this com- of this species was studied [24]. It was shown that pound; a procedure for more economical determi- an increase in the time of ultrasonic treatment nation of flavons was proposed [28, 29]. during the extraction of flavonoids with a 60 % Two new components for the genus were aqueous solution of ethanol promotes an increase identified with the help of UV spectrophotometry in the yield of flavonoids from 3.83 to 11.23 %. It and mass spectrometry: 7-О-β-L-arabinopyrano- should be stressed that the content of phenol syl(1-6)β-D-glucopyranoside of luteolin and compounds in the abscissed leaves of the species 7-О-β-D-xylopyranosyl(1-6)β-D-glucopyranoside of Salix genus growing in India was studied of luteolin. For S. raddeana, also the following previously. It was discovered that the maximal compounds were reported: 7-О-β-D-xylopyrano- amount of flavonols is characteristic of dead syl(1-6)β-D-glucopyranoside of diosmetine, rutin, leaves [25]. astragalin and isoquercetin [30–33]. Salix alba Salix caprea S. alba L. is white willow belonging to the S. caprea L. (= S. hultenii Flod.) is goat willow Salix section of Salix subgenus. It is a large tree belonging to the Vetrix section of Vetrix subgenus. up to 30 m high. The species is widespread in It is a tree up to 12–15 m high. It grows in forests, culture. The natural habitat occupies the major on clearings, at forest edges, near roads. The part of Europe; there are data on its occurrence species is widespread over the territory of Eurasia. in northern Africa, West and Middle Siberia, The following phenol compounds were found Middle Asia, Kazakhstan. in the wood and tree warts of goat willow: vanillic White willow is one of the best studied species, acid, catechine, gallocatechine, dihydrokaempferol, it is used in scientific and practical medicine [4]. dihydromyricitin, naringenin and taxifolin. It was The extract of the bark is known to contain established that warts and branches contain eryodistiol, 5,7-dihydroxychromen-4-one and higher concentrations of the substances than the naringenine. These data were obtained using stem of the same tree [34]. A procedure of an high-rate chromatography, mass spectrometry easier and rapid extraction of phenol compounds and NMR spectroscopy [26]. Investigation of was developed for the blossom clusters of goat water extracts from the bark of white willow and willow as example: an optimal version is the use other species is carried out at the Pyatigorsk of 50 % methanol, the ratio of the mass of raw State Pharmaceutical Academy. It was revealed material to the solvent mass should be 1 : 40, that the content of extractives is the highest in boiling time 3 h with a reflux condenser. The the extract prepared by the authors according to yield of flavonoids reached 26.82 mg/mL [35]. the XI edition of the State Pharmacopeia A comparative study of S. caprea and S. published in 1987 [27]. This extract of the bark of repens L. (Vetrix subgenus, Incubaceae Kerner white willow possessed high antiinflammatory section) species and their hybrids was carried out activity. in 2003 in Sweden [36]. It was established that a high level of condensed tannines and low level of Salix raddeana phenol glycosides is characteristic of S. caprea; for S. repens, quite contrary, the level of tannines S. raddeana Laksch. ex Nasarow is Radde is low and the level of phenol glycosides is high. willow belonging to section Vetrix Dumort. of the Hybrids occupy an intermediate position in the Vetrix subgenus. It is a high bush or a tree up to content of phenol compounds. A similar 6–8 m high. The species is widespread in forests, investigation was also carried out for the species forest-steppe and lower mountainous belts in from North America, subgenus Vetrix: S. sericea Eastern Siberia, in the Far East, in the northern Marshall (Griseae (Borrer) Barratt ex Hooker and north-eastern regions of Mongolia, China and section), S. eriocephala Michx. (Cordatae Barratt Korea. ex Hooker section) and their F1 hybrids [37, 38]. 464 A.