Chemotaxonomy studies on the genus Hedysarum

Highlights

• Sect. Fruticosa was much different from the three other sections, while sect. Multicaulia was closer to sect. Subacaulia.

• Isoflavonoids and pterocarpanes were proved to be the common constituents of genus Hedysarum.

• Pterocarpenes, benzofurnans, and coumestans were the characteristic constituents of sect. Fruticosa.

• Chalcones were the chemical marks of sect. Multicaulia and sect. Subacaulia.

Abstract

In combination with phytochemical results, the pilot chemotaxonomy study on genus Hedysarum by using HPLC methods revealed differences between section Fruticosa and the three other sections Multicaulia, Obscura and Subacaulia, but there was a closer genetic relationship with Multicaulia and Subacaulia. Isoflavonoids and pterocarpans were proved to be the common constituents of genus Hedysarum, whereas pterocarpans, benzofurans, and coumestans were the characteristic constituents of section Fruticosa, and chalcones were the chemical markers of section Multicaulia and section Subacaulia. The present finding is consistent with the classical morphological classification of genus Hedysarum, and provides supporting evidences for dividing Hedysarum into two subgenera, i.e. subgenus Hedysara and subgenus Ruticosa.

Introduction

The genus Hedysarum Linn., established in 1753 by Linneaus, is the largest genus of tribe Hedysareae (Papilionoideae, Leguminosae).There are about 160 Hedysarum species in the world, of which 41, assigned to four sections of section Fruticosa B. Fedtsch., section Multicaulia Boiss., section Obscura B. Fedtsch., and section Subacaulia Boiss., are distributed in China throughout the dry and cold area of inner land and in Himalaya area (Xu, 1998). In China, some Hedysarum roots have been used as restorative foods or herbal medicines. Of these, Hedysari Radix (“红芪” Hongqi in Chinese), the dry roots of H. polybotrys Hand. –Mazz., is a famous traditional Chinese medicine (TCM) which has been widely used to reinforce “Qi” (vital energy) and for the treatment of various diseases (Chinese Pharmacopoeia Commision, 2015). Other medicinal Hedysarum roots are sometimes used as the substitute for Hedysari Radix in local regions (Committee of Chinese Materia Medica of National Administration, 1999). As far as the classification of Hedysarum is concerned, different opinions are still present. Some scholars suggested that two subgenus, i.e. subgenus Hedysara and subgenus Ruticosa, should be set up in genus Hedysarum (Sa and Zhao, 2001). In order to get an overall understanding of the chemical constituents and provide further chemotaxonomic evidences for genus Hedysarum, our group has carried out a systematical investigation on the chemical constituents of Hedysarum roots, including H. polybotrys, H. semenovii Regel et Herd., H. kirghisorum B. Fedtsch., H. gmelinii Ledeb. and H. multijugum Maxim. A variety of compounds, including isoflavonoids (Hai et al., 2003; Liu et al., 2005a, 2006a; 2009b; Wang et al., 2017), pterocarpans (Wang et al., 2002, 2003), coumestans (Wang et al., 2007), benzofurans (Wang et al., 2006), chalcones (Liu et al., 2005b, 2018), oleanane saponins (Liu et al., 2006b, 2009a), and bisepoxylignan (Hai et al., 2003), have been isolated and characteristic chemical features of Hedysarum species are revealed. In this paper, systematic chemical analysis of seven representative herbs from four sections of genus Hedysarum, including H. polybotrys, H. semenovii, H. kirghisorum, H. sikkimense Benth. ex Baker, H. gmelinii, H. ferganense Korsh. and H. multijugum (Table 1), was performed by using HPLC-DAD methods in order to elucidate the chemical profiles and provide evidences for taxonomic division of Hedysarum species.