Alkaloids as chemotaxonomic markers from the Philippine endemic Uncaria perrottetii and Uncaria lanosa f. philippinensis

1 Introduction

The genus Uncaria Schreb. (Rubiaceae) has been described commonly as lianas with characteristic paired fang hooks at the nodes (Ridsdale, 1978). The species are widely distributed among tropical areas such as Southeast Asia, Africa, and South America (Ridsdale, 1978). Uncaria species possessed interesting chemical structures including alkaloids, terpenes, quinovic acid glycosides, flavonoids and coumarins (Heitzman et al., 2005). Biological activities associated with various Uncaria species include cytotoxicity, anti-inflammatory, antiviral, immune-stimulant, antioxidant, CNS-related response, vascular, hypotensive, mutagenicity and antibacterial properties (Heitzman et al., 2005). A total of 34 Uncaria species are recorded worldwide (Ndagijimana et al., 2013). In the Philippines, the genus Uncaria was represented by ten species in which two, U. nervosa Elmer and U. perrottetii (A. Rich.) Merr. are endemic (Ridsdale, 1978). U. perrottetii is an interesting Philippine endemic as it is the only species in the genus that bears a deeply bifid laciniate stipule and a distinct violet colored shoot system.

In our continuing studies on the endemic Philippine Rubiaceae species (Tan et al., 2012; Tan et al., 2014a,b), we herein report the isolation and identification of oxindole alkaloids from the leaves of U. perrottetii and U. lanosa f. philippinensis. The structures were elucidated based on 1D and 2D NMR, MS and by comparison with literature data. This is the first phytochemical study on U. perrottetii and U. lanosa f. philippinensis. The isolated alkaloids also served as chemotaxonomic markers for the different Uncaria species.

2 Materials and methods

3 Results and discussion

Chromatographic purification of the crude base of U. perrottetii yielded uncarine A or isoformosanine (1), uncarine E or isopteropodine (2), and rauniticine-allo-oxindole A (3) (Fig. 1). This is the first report of alkaloids 1 and 3 from U. perrottetii while uncarine E (2) was previously identified from this plant (Lleander et al., 1974). The presence of 2 was also identified from U. bernaysii, U. donisii, U. guaianensis, U. homolalla, U. laevigata, U. lanosa, U. longiflora, U. orientalis, U. roxburghiana, U. scandens, U. sinensis, U. sterrophylla, U. tomentosa, and U. veluntina (Arbain et al., 1993; Aquino et al., 1997; Kam et al., 1991; Lee et al., 1999a, 1999b; Phillipson et al., 1978; Tanahashi et al., 1997; Wagner et al., 1985). From the 34 species, alkaloid 3 was previously identified from U. elliptica (Phillipson and Supavita, 1983). Uncarine A (1) was previously identified from U. attenuata, U. cordata, U. gambir, U. hirsuta, U. laevigata, U. orientalis, and U. sessilifructus (Phillipson et al., 1978; Wu and Chan, 1994).

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Fig. 1

Structures of isolated alkaloids.

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U. lanosa f philippinensis has elaborated isomitraphylline (4), mitraphylline (5), formosanine or uncarine B (6), uncarine F (7), corynoxine (8), and uncarine D or speciophylline (9) (Fig. 1). Isomitraphylline (4) was isolated from 18 species namely U. africana, U. bernaysii, U. callophylla, U. elliptica, U. guianensis, U. hirsuta, U. homomalla, U. laevigata, U. lancifolia, U. lanosa, U. longiflora, U. orientalis, U. perrottetii, U. scandens, U. sessilifructus, U. sterrophylla, U. tomentosa, and U. veluntina (Diyabalanage et al., 1997a, 1997b; Phillipson et al., 1978; Tantivatana et al., 1979; Wagner et al., 1985). The presence of mitraphylline (5) was perceived in U. africana, U. attenuata, U. bernaysii, U. callophylla, U. elliptica, U. gambir, U. guianensis, U. hirsuta, U. homomalla, U. laevigata, U. lancifolia, U. lanosa, U. longiflora, U. orientalis, U. perrottetii, U. scandens, U. sessilifructus, U. sterrophylla, U. tomentosa, and U. veluntina (Phillipson et al., 1978; Wagner et al., 1985; Tantivatana et al., 1979; Tantivatana et al., 1980; Herath et al., 1978). The species U. attenuata, U. elliptica, U. gambir, U. hirsuta, U. laevigata, U. orientalis, and U. sessilifructus were known to contain uncarine B (6) (Phillipson et al., 1978; Wu and Chan, 1994; Tantivatana et al., 1980; Herath et al., 1978). Uncarine F (7) was previously identified from U. bernaysii, U. donisii, U. homomalla, U. lanosa, U. longiflora, U. orientalis, U. perrottetii, U. roxburghiana, U. scandens, U. sessilifructus, U. sinensis, U. sterrophylla, and U. veluntina (Phillipson et al., 1978; Tanahashi et al., 1997). Six species contained corynoxine B (8) including U. attenuata, U. cordata, U. kunstleri, U. macrophylla, U. sessilifructus, and U. sterrophylla (Phillipson et al., 1978; Lee et al., 2000). Uncarine D (9) was isolated from U. attenuata, U. bernaysii, U. donisii, U. guianensis, U. homomalla, U. laevigata, U. lanosa, U. longiflora, U. orientalis, U. perrottetii, U. roxburghiana, U. scandens, U. sinensis, U. sterrophylla, U. tomentosa, and U. veluntina (Arbain et al., 1993; Phillipson et al., 1978; Tanahashi et al., 1997).

Except for rauniticine-allo-oxindole A (3), all the alkaloids from this study were identified from at least six different Uncaria species. Thus, the isolated alkaloids may provide as chemotoxanomic markers for the genus Uncaria.

Löfstrand et. al. (2014), supported the monophyly (PP = 1.00; BS = 100%) of Uncaria indicating the distinctness of members of the genus from other members of the family Rubiaceae. It must be noted that only members of Uncaria exhibit the following character combinations: (1) lianescent growth habit and (2) presence of paired fang hooks at the nodes. This distinctness can be directly correlated to the presence of unique oxindole alkaloids in Uncaria, which are of chemotaxonomic significance. Phylogenetically, Löfstrand et al. suggested that members of the genus can be subdivided into an Asian and Afro-Neotropical clades. It is no surprise that U. perrottetii and U. lanosa f. philippinensis share oxindole alkaloids with other members, as they are representatives from the strictly Asian clade. These alkaloids, therefore, maybe be used to delimit members of the clade.