Marsdenieae Benth.

2.8. Marsdenieae

We sampled 26 species from 10 of 27 genera of tribe Marsdenieae. Compounds fragmenting to m/z 120 and 138 were present in samples of Marsdenia tinctoria R.Br. and Marsdenia glabra Constantin (Table 2). However, three of these four ions have a molecular mass of 432.5, raising the possibility that these are structurally similar to the aminobenzoyl glycoside previously identified in Wrightia antidysenterica (Srinroch et al., 2019) (Fig. 5) rather than PAs. HRMS would need to be used to determine if the m/z 432 ions observed in Marsdenia and Wrightia species are the same compound. Thus we have moderate confidence in the presence of PAs only in the one sample of M. glabra, based on the presence of an m/z 388.2 ion.

The current taxonomic concept of Marsdenia R.Br. is highly polyphyletic (Rodda et al., 2020), and the segregation of monophyletic genera from Marsdenia sensu lato is ongoing (Espírito Santo et al., 2019). Marsdenia tinctoria (the type species) and M. glabra belong to the small group of species segregated as Marsdenia sensu stricto (Bullock, 1956; Forster, 1995). The most frequently reported natural products from species of Marsdenia sensu lato and other genera of Marsdenieae are steroids, steroidal alkaloids, and steroidal glycosides including the antisweet gymnemic acids from the medicinal plant Gymnema sylvestre (Retz.) R.Br. ex Sm. (Liu et al., 1992). Phenanthroindolizidine alkaloids are rare, reported only from Telosma pallida (Roxb.) Craib (Mulchandani and Venkatachalam, 1976). All three common classes of compounds have been previously reported from M. tinctoria (Chowdhury et al., 1994; Gao et al., 2009). Marsdenia tinctoria is also a source of indigo (Mohd Nasuha and Choo, 2016), although the chemical origin of the stain has not been identified in this species.