Stigmasterol from a Pandanus and Myrmecodia species

The isolation of compounds 1 and 2, respectively from two unrelated plants [a Pandanus (Pandanaceae) and a Myrmecodia (Rubiaceae)] is presented. According to the Nuclear Magnetic Resonance (NMR) spectroscopy, both biomolecules could be a triterpene. The NMR data from P. tectorius' phytosterol was compared, where a mixture of stigmasterol:β-sitosterol (2:1) was reported. However, the signals for an exo-methylene group likewise in Pandanus' antitubercular tirucallane, did not appear in the ¹H-NMR spectrum of 1 and 2 (500 MHz, δH 0.5–5.5 ppm, CDCl3). Furthermore, the ¹³C-NMR spectroscopy (125 MHz, δC 10–141 ppm, CDCl3) suggested 1 and 2 as a non-ketosteroid of possibly 29 carbon atoms. Both equally could be an aglycon triterpenoid, due to the absence of ¹³C-NMR signals at δC 60–110, which are carbons' signals, assigned for sugar moieties. However, one ¹³C-NMR peak at δC 71.81 and 71.82 [C-3 (OH)] was detected, respectively for 1 and 2. Therefore, the occurrence of a hydroxylated stigmastane-like molecule was proposed. Instead, two sets of -C=C- bonds (1: δC 140.76; 129.29 and 138.29; 121.70); (2: δC 140.78; 129.31 and 138.29; 121.70) were observed. From 2D NMR spectra, 1 was recognised as stigmata-(5,22)-diene-3-ol or stigmasterol. Stigmasterol was also reported from a Hydnophytum species, another epiphytic myrmecophytes associated with Myrmecodia. Recrystallizations were performed to purify crystal 2 (13.4 mg colorless needles; Rf = 0.2), which was also proposed as a type-1 molecule. In short, stigmasterol was identified as the major non-polar component from these two plant extracts.