**4. Conclusions**

Based on our investigation carried out on the identity of the plant, and a re-examination of the voucher specimen (Rimachi # 12161) at the MOBOT, it can now be concluded that this species should be treated only as an unidentified species of *Machaerium* Pers., as determined by the collection information (Manuel Rimachi, Y. 12161). This appears to be the first report of macharifurogerol (**1a**) and its epimer **1b** from a natural source. In addition, the isolation of isoflavons (**2** and **3**) and pterocarpans (**4** and **5**) from this *Machaerium* species (Rimachi 12161) illustrated that these isoflavonoids are typical chemotaxonomic markers of the genus *Machaerium* [11,12]. Machaeriols and its biogenetic precursor machaeridiols are only isolated from this species (#12161) from the genus *Machaerium*, which are analogous to hexahydrocannabinol (HHC) and dihydrocannabidiol base skeletons of *Cannabis* and its variants, in higher plants [6]. The only other bibenzyl analogue of Δ9-THC, perrottetinen, was previously reported from the liverwort *Radula perrottetii* [20]. It is intriguing to note that the strong MRSA and VRE inhibitory activities, together with their antiparasitic activities [5,6] of the isolated compounds of *Machaerium* (12161) is contributed by HHDBP machaeriols and their 5,6-*seco* analogs machaeridiols. The stereo-specific total synthesis of machaeriol A-D (**6**–**9**) and mechaeridiol B (**12**) was reported [21–24]. In addition, analogs of machaeriols and related HHC were recently synthesized, which showed anticancer activity [25]. It was anticipated that these phytocannabinoids could serve as potential template for anti-MRSA and anti-VRE lead candidates, because of their inherent inhibitory activities alone, as well as strong synergistic activity when tested in combination with machaeriol and machaeridiol. The observation of significant activity in permeabilized multidrug resistant Gram-negative pathogens, also offers the potential for optimization of the chemical scaffold to generate analogues with better cell permeability. These compounds might provide important new leads for WHO priority Gram-negative bacterial pathogens.

**Supplementary Materials:** The following are available online, NMR and HRMS spectra (Figures S1–S11) of compound **1**, and Table for NMR data (Table S1) of compounds **2**–**5** are provided in supporting information.

**Author Contributions:** I.M., J.M.S., and K.M.R., conceptualized the study; I.M., M.A.I., M.K., and J.Z., planned the experiments and spectral analysis for chemistry work; M.W., execute LCMS work; M.R.J., planned antimicrobial and Checkerboard assay at UM; J.M.S., C.H., M.C., B.M., and T.A.-A., executed antimicrobial work at KCL and PHE; V.R., and I.M., authenticated and provided critical information on plant authentication; M.A.I., M.R.J., M.A.I., V.R., M.W., J.Z., J.M.S., and K.M.R., prepared the original draft of the manuscript. All the authors contributed to the writing and editing of the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported in part by the USDA Agricultural Research Service Specific Cooperative Agreement No. 58-6060-6-015, and the NIH, NIAID, Division of AIDS, grant no. AI 27094. Work at PHE was supported by Grant in aid funding through an Open Innovation programme (Project 111742).

**Acknowledgments:** The authors sincerely thank Manuel Rimachi Y. and (Late) Sydney T. McDaniel (Mississippi State University) for the collection of plant material; Andrew Townesmith, Missouri Botanical Garden, St. Louis, MO, USA; Andrew Sanders, UCR Herbarium, California, USA; and Fabiana Filardi, Instituto de Pesquisas Jardim Botânico do Rio de Janeiro, Brazil, for their expert opinion on the voucher specimen. Marwa Hasan, Y. Wang, F. Wiggers, and M. Wright, NCNPR, UM, for assisting and conducting chemistry work, HRMS, NMR experiments and biological assays, respectively.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


**Sample Availability:** Samples of the compounds **1**–**8** and **10**–**12** are available from the authors.

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