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Ants are perhaps not the first organism one would turn to for medical assistance, but researchers in Hong Kong and Japan have now used IR and NMR spectroscopy to study the absolute structures of compounds extracted from Chinese medicinal ants that are thought to have anti-arthritic activity and be beneficial in treating hepatitis. Zhi-Hong Jiang and Qing-Xiong Yang in the School of Chinese Medicine, at Hong Kong Baptist University, in Kowloon Tong, People's Republic of China and Takashi Tanaka and Isao Kouno of the Department of Molecular Medicinal Sciences, at Nagasaki University, Japan, reveal two new bicyclic polyketide lactones from the ant species Polyrhachis lamellidens Smith. The Chinese medicinal ant has been used clinically as a folk medicine for many years in treating rheumatoid arthritis and hepatitis, the researchers explain. In earlier research, they successfully demonstrated the analgesic and anti-inflammatory effects of its ethanol extracts, which substantiated the role of the ant in folk medicine. Elsewhere, various alkaloids and peptides have been isolated from African and Australian ants, but Kouno and colleagues are the first to report on chemical studies of this Chinese species. The team obtained 2 kilograms of ants from the Jinling Ants Therapy Research Center, Nanjing, China, and the species was confirmed by Jian Wu of the Chinese Academy of Forestry, in Beijing, China. The researcher then investigated the ether fraction of methanol extracts of P. lamellidens, isolating polyrhacitide A as an optically active material forming colourless needle-like crystals. Mass spectrometry and 13C NMR data proffered the molecular formula C18H32O5. They then utilised IR spectroscopy to reveal the nature of the compound's unsaturation. One of three degrees of unsaturation was attributed to an ester carbonyl absorbing at 1729 cm-1 as well as the sp2 carbon signal at delta 169.2. "The remaining two degrees of unsaturation were attributed to two ring units in the molecule because no other unsaturated carbon signal was observed in the 13C NMR spectrum," the researchers add. NMR also revealed five oxygenated methine signals, one methyl group, and 11 methylene signals. By analysing cross-peaks in the 1H-1H COSY spectrum and data from 1D NMR and HSQC spectra further structural details were disclosed, ultimately revealing a lactone structure. HMBC correlations then revealed a linear alkyl structure between the 12th and 18th carbon atoms and this information combined with the unsaturation insights allowed them to characterize the molecule as a bicyclic lactone with a hydroxylated alkyl group. A similar approach to the white powder of polyrhacitide B revealed its absolute structure too. The researchers point out that compounds related to the two novel polyketide lactones, polyrhacitides A and B, occur elsewhere in nature in plants of the Lamiaceae (mint family), Lauraceae (laurel family), and Staphyleaceae (which includes bladdernut tree), which they suggest indicates their significance in the study of chemical ecology. These plants have also been indicated in treating inflammatory conditions. Whether or not other ant species (Formicidae) will yield equally medicinal extracts remains to be seen. However, lessons can be learned regarding the harvesting of traditional knowledge from traditional forms of medicine as well as the need to conserve biodiversity the world over. Related links:
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