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, δ_H 0.5-5.5 ppm, CDCl₃). Furthermore, the ¹³C-NMR spectroscopy (125 MHz, δ_C 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 δ_C 60-110, which are carbons´ signals, assigned for sugar moieties. However, one ¹³C-NMR peak at δ_C 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: δ_C 140.76; 129.29 and 138.29; 121.70); (2: δ_C 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; R_f = 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.