The genus Amorpha (Fabaceae) including 16 species is native to North America with a center of diversity in the southeastern United States [1] . Among them, A. fruticosa (Figure 1) which has been used as a Chinese folk medicine for the treatment of burn, ambustion, carbuncle and eczema [2] is the only one species introduced into China (Zhao, 1982) [3] . Up to now, chemical investigations of genus Amorpha mainly focused on A. fruticosa, which resulted in the isolation of more than forty compounds, including stilbenes [4] , rotenoids [5] and flavanones

[6] , as well as isoflavones [7] . The three former groups are also found in the other species of this genus [8] - [10] . Our previous study on the EtOAc partition of 95% EtOH extract of the seeds of A. fruticosa has resulted in the isolation of eight rotenoid glycosides [11] . In this paper, the isolation and characterization of seventeen compounds from its n-hexane partition were reported. Among them, one compound was firstly purified as a natural product, nine were isolated from the genus Amorpha for the first time, and one was obtained from the Fabaceae family initially. The presence of these compounds suggests that genus Amorpha and Dalbergia may have very close chemotaxonomic relationship, and shows the relationship between this plant and other species from the Fabaceae family.

The isolated compounds were identified as 6aR, 12aR-dalbinol (1) [12] , amorphigenin (2) [12] , 12a-hydrox- ydalpanol (3) [12] , 6aS, 12aS-dalbinol (4) [12] , 12a-hydroxymunduserone (5) [13] , amorphispironone (6) [14] , ononin (7) [15] , isoformonentin (8) [16] , daidzein (9) [17] , prunetin (10) [18] , pratensein (11) (Dixit et al., 2012) [19] , 7-O-β-D-glucopyranosyl-7-hydroxy-2’,4’,5’-trimethoxyisoflavone (12) [20] , 7-hydroxy-2’,4’,5’-trimetho- xyisoflavone (13) [21] , amorfrutin B (14) [22] , gallic acid (15) [23] , 4-methoxygallic acid (16) [24] and 3,4-dimethoxygallic acid (17) [25] , respectively, on the basis of their ¹H NMR and ¹³C NMR spectra analysis and comparison with those reported data in the related literatures (Figure 2). The absolute configurations of 6a and 12a of 1-3 and 5 were assigned as R,R based on the CD data which revealed a negative Cotton effect at 326 nm, while 4 was S,S with mirror image CD spectrum of 1 (Figure 3) [11] .

The present study reported the isolation and structure elucidation of seventeen secondary metabolites from the seeds of A. fruticosa, including six rotenoids (1-6), seven isoflavones (7-13), one stilbene (14) and three benzoic acid derivatives (15-17). Among them, compound 4 was firstly purified as a natural product, compounds 5, 8-12 and 15-17 were isolated from the genus Amorpha for the first time, and compound 17 was obtained from the

Fabaceae family initially. Although compound 12 has been once reported, it has no CAS number yet. Compounds 1-3, along with the previous reported compounds amorphin and 8’-O-β-D-glucopyranosyl-amorphigenin, have been isolated or detected in ten species of the genus Amorpha (A. fruticosa, A. angustifolia, A. canescens, A. frangrans, A. californica, A. glabra, A. mierophylla, A. nana, A. croceotanata, and A. caroliniana) [9] at the same time, which provides a chemotaxonomic evidence to support the morphological classification of this genus.

Rotenoids 1-2 and isoflavones 12-13, as well as our previous reported rotenoid glucosides 8’-O-β-D-gluco- glucopyranosyl-amorphigenin and dalbin [11] , were also isolated from Dalbergia monnetaria (Fabaceae) simultaneously [20] . Such a coincidence should be explained by the fact that the isoflavone 13 was the key intermediate during the biosynthesis of its corresponding rotenoids [26] . In addition, some compounds obtained in this studyalso exist in other species of genus Dalbergia, as follows: compound 1 in D. nitidula [27] ; compound 7 in D. paniculata [28] and D. odorifera [15] ; compound 9 in D. odorifera [17] , D. parviflora [29] , D. frutescens [30] , D. ecastophyllum [31] , D. stevensonii [32] and D. ecastophylla [33] ; compound 10 in D. odorifera [34] , D. sympathetic [18] , D. sissoo [35] and D. spinosa [36] ; compound 11 in D. sissoo [19] , D. parviflora [37] and D. odorifera [38] ; compound 13 in D. vacciniifolia [21] . All these suggested that genus Amorpha and Dalbergia may have very close chemotaxonomic relationship.

Furthermore, compounds 1 and 2 were also synchronally isolated from Berchemia discolor [39] , compound 3 was once obtained from Aeschynomene indica [40] , and compound 5 was obtained from Pachyrrhizus erosus [13] , Tephrosia fulvinervis [41] and Tephrosia pentaphylla [41] , which exhibit the relationships between A. fruticosa and these species, all belonging to family Fabaceae except Berchemia discolor (Rhamnaceae). Compound 4 was isolated naturally for the first time, while compounds 6 and 14 both only existed in A. fruticosa. Compounds 15 and 9 widely distributed in the family Fabaceae, and compound 16 has only been isolated from one species of it (Canavalia gladiate) [42] , while it is the first time to obtain compound 17 from this family. Therefore, compounds 4, 6, 14 and 17 should be served as chemotaxonomic markers for A. fruticosa.

According to the above results, our present study extends the knowledge about the compounds of genus Amorpha and confirms Dalbergia as its chemotaxonomic related genus.

This work was supported by the National Natural Science Foundation of China (81503226) and the Doctoral Fund of Guangdong Medical College (XB1301).

Xin Wu,Hongbo Liao,Kefeng Wu,Liao Cui, (2016) Chemical Constituents from the Seeds of Amorpha fruticosa and Their Chemotaxonomic Significance. Open Access Library Journal,03,1-7. doi: 10.4236/oalib.1102740