Chinese Journal of Natural Chinese Journal of Natural Medicines 2016, 14(5): 03210334 Medicines doi: 10.3724/SP.J.1009.2016.00321 Recent advances in phytochemistry and pharmacology of C21 steroid constituents from Cynanchum plants GU Xiao-Jie*, HAO Da-Cheng Biotechnology Institute, School of Environment, Dalian Jiaotong University, Dalian 116028, China Available online 20 May, 2016 [ABSTRACT] Cynanchum is one of the most important genera in Asclepiadaceae family, which has long been known for its therapeutic effects. In this genus, 16 species are of high medicinal value. The extracts of the root and/or rhizome parts have been applied in traditional Chinese medicines (TCM) for the prevention and treatment of various illnesses for centuries. C21 steroids, as the typical constituents of Cynanchum species, possess a variety of structures and pharmacological activities. This review summarizes the comprehensive information on phytochemistry and pharmacology of C21 steroid constituents from Cynanchum plants, based on reports published between 2007 and 2015. Our aim is to provide a rationale for their therapeutic application, and to discuss the future trends in research and development of these compounds. A total of 172 newly identified compounds are reviewed according to their structural classifications. Their in vitro and in vivo pharmacological studies are also reviewed and discussed, focusing on antitumor, antidepressant, antifungal, antitaging, Na+/K+-ATPase inhibitory, appetite suppressing and antiviral activities. Future research efforts should concentrate on in vitro and in vivo biological studies and structure activity relationship of various C21 steroid constituents. [KEY WORDS] Asclepiadaceae; Cynanchum; C21 steroid constituents; Phytochemical studies; Pharmacological actions [CLC Number] R284 [Document code] A [Article ID] 2095-6975(2016)05-0321-14 immune deficiency, and other illnesses. A survey of the Introduction literature shows that C21 steroids are typical constituents of [2] Cynanchum species have long been used in traditional Cynanchum species . Phytochemical studies of Cynanchum Chinese medicine (TCM). This genus comprises of about 200 species have resulted in the isolation of numerous biologically species in Asclepiadaceae family and is distributed worldwide, active C21 steroidal compounds. Most of them possess a including east Africa, the Mediterranean region, the tropical variety of pharmacological actions, e.g. antitumor, antiaging, zone of Europe, and the subtropical and temperate zones of antidepressant, antifungal, and antiviral activities, and also [3] Asia. There are 53 species and 12 varieties are native to appetite suppressing ability . Due to their relatively rich southwestern region of China. Among them, 16 species, medicinal value, C21 steroids deserve more research than they including C. auriculatum, C. atratum, C. glaucescens, C. have received. Several monographs on Cynanchum species bungei, C. chekiangense, C.vincetoxicum, C. saccatumi, C. have been published. Wu et al and Liu et al have summarised inamoenum, C. mongolicum, C. otophyllum, C. paniculatum, the chemistry and pharmacological activities of Cynanchum [4-5] C. stauntonii, C. decipines, C. wallichii, C. wilfordii, and C. plants in two consecutive reviews . Wu and Zhou have [1] versicolor, are of high medicinal value . The extracts of the contributed a review on the chemical constituents of C21 root and/or rhizome parts have long been used in folk steroids, alkaloids, flavonoids, terpenoids, phenols, and other [6] medicine to treat rheumatalgia, phlegm, geriatric diseases, ingredients in plants of Cynanchum . The classification, NMR spectral characteristics and structure determination of Cynanchum C21 steroid constituents are covered in the monograph by Bai et al [7]. Ni and Ye have reviewed the [Received on] 04-Jun.-2015 distribution and pharmacological activities of C steroidal [Research funding] This work was financially supported by the 21 [8] National Natural Science Foundation of China (No. 21502014). glycosides in in plants of Asclepiadaceae . Although five [*Corresponding author] Tel: 86-411-84105506, E-mail: guxiaojie review articles on certain aspects of C21 steroids have [email protected] appeared, no recent review has been published since. The These authors have no conflict of interest to declare. purpose of this comtribution was to review the up-to-date – 321 – GU Xiao-Jie, et al. / Chin J Nat Med, 2016, 14(5): 321334 literatures covering phytochemical and pharmacological of hydroxyls at C-3, can be grouped into four types, viz., aspects of naturally occurring plant C21 steroids and to discuss types B, C, D, and E. According to the different pregnane the future directions as well. skeletons, these compounds can be finally divided into five types: the normal four-ring pregnane type (A), 14,15-seco- Phytochemistry pregnane type (B), 13,14:14,15-diseco-pregnane type (C), the aberrant 14,15-seco-pregnane type (D), and 12,13-seco-14, C21 steroid constituents possess a tetracyclic pregnane carbon skeleton and differ in the number and nature of 18-nor-pregnane type (E) (Fig. 1). In C21 steroidal glycosides, substituents and sometimes in the degree of unsaturation, the sugar moiety is linked most frequently at C-3 to a which are found in Cynanchum species either in free states hydroxyl group of the pregnane aglycone, containing one to or as glycosides. They can be classified into two groups on seven sugar units with the mode of 1→4, and generally is the basis of the carbon framework: typical C21 steroids and composed of a linear rather than a branched oligosaccharide modified C21 steroids. The former, usually designated as chain. The most common sugar residues are hexose type A, is characterized by the common pregnane skeleton. (glucose), 6-deoxyhexose (thevetose), and 2,6-dideoxyhexoses The latter, containing the unusual modified pregnane (cymarose, oleandrose, digitoxose, diginose, sarmentose, and skeleton and fewer hydroxy groups except for the location canarose) (Fig. 2). – 322 – GU Xiao-Jie, et al. / Chin J Nat Med, 2016, 14(5): 321334 Fig. 1 Basic skeletons of C21 steroidal glycosides from Cynanchum species Fig. 2 Chemical structures of sugar moieties Normal four-ring pregnane type substituted by a cinnamoyl group [14]. Type A, including compounds 1−59, can be further 14, 15-Seco-pregnane type classified into three subtypes, based on different oxidation Type B, including 14 new steroidal glycosides, is patterns and specific substituent groups at C-8, C-12, C-17 characterized by a tetrahydrofuran unit as the D-ring and and C-20 (Table 1). Substituents at C-12, C-17 and C-20 C-16 and C-18 are joined to C-20 through a five-membered are always esters, with the hydroxyl groups of the cyclic ether linkage (Table 2). According to the number and aglycone at these positions esterified with six different position of unsaturated groups and hydroxyls, type B is acyl groups (Fig. 3). Type A1 is the largest group and further classified into four subtypes. Type B1, including currently comprises of 50 new compounds. These 60−65, possesses the common deoxyamplexicogenin A [26-28] members consist of six different aglycones on the basis of skeleton ; type B2, including 66−71, is anhydro- six different acyl groups at C-12 and C-17, viz., kidjoranin hirundigenin derivatives [26, 29]; and aglycones of the other (1−9), metaplexigenin (10 and 11), deacylmetaplexigenin types, 72 (type B3) and 73 (type B4), are stauntogenins A (12−16), 17-O-acetyl-kidjoranin (17), qinyangshengenin and B, respectively [26]. (18−32), and caudatin (33−50) [9-24]. The different 13,14:14,15-Diseco-pregnane type oxidation patterns on C-20 make A1 distinguish from A2. Steroid constituents of type C have nine-membered Type A2 consists of 6 new compounds: 51−53 from kidjoranin unsaturated lactone ring with the oxidation and the breakdown steroidal aglycone [14], 54 and 55 from 20-O-acetylpenupogenin of C- and D-rings, and contain 59 new examples (Table 3). steroidal aglycone [24], and 56 from 2′,3′-Z-gagaminine Because of the different configurations and positions of [15] steroidal aglycone . Type A3 (57) differs from A2 in a hydroxyl groups, a total of 49 new steroids from type C1 have hydroxy group at C-8 that is oxidized into a carbonyl [15]. been described: 74−90 from glaucogenin C, 91−116 from Type A4 (58) differs from A1 in a hydroxy group at C-3 glaucogenin A, 117−119 from 2-epi- glaucogenin A, 120 that is eliminated to form double bonds [14]. The formation from glaucogenin E, 121 from neocynapanogenin F, and 122 [26, 27, 29-39] of type A5 (59) is due to elimination of H2O by the two from hancopregnane . Type C2 consists of 4 new hydroxyl groups at C-12 and C-20, and its hydroxyl group compounds, and is based on the amplexicogenin B (123 [40] [33, 41] of C-17, a commonly free group in pregnane sapogenin, is and 124) and C (125 and 126) skeletons . Type C3 – 323 – GU Xiao-Jie, et al. / Chin J Nat Med, 2016, 14(5): 321334 Table 1 C21 steroid constituents isolated from Cynanchum species (A type) No. Type Compound Substitutional group Taxon Ref. 1 A1 Cynauricoside A R1 = RC1 R2 = RX1 R3 = H a 9 2 A1 Cynauricoside B R1 = RE1 R2 = RX1 R3 = H a 9 3 A1 Cynauricoside C R1 = RE2 R2 = RX1 R3 = H a 9 4 A1 Wilfoside K1GG R1 = RF1 R2 = RX1 R3 = H b 10 Rostratamine-3-O-β-D-oleandropyranosyl-(1→4)-β- 5 A R = RC R = RX R = H d 11 1 D-cymaropyranosyl-(1→4)-β-D-cymaropyranoside 1 3 2 1 3 6 A1 Auriculoside Ⅲ R1 = RG5 R2 = RX1 R3 = H a 12 7 A1 Auriculoside Ⅳ R1 = RF1 R2 = RX1 R3 = H a 12