A Novel 8-Carbon Keto Saccharide Backbone from Roman Chamomile (Chamaemelum nobile L.)

Chamaemelum nobile (L.) Allioni, (syn. Anthemis nobilis L. or Chamomilla nobilis G.) is a perennial herb of the Asteraceae family, with the common name Roman chamomile. The plant has been widely used as household medicine for the treatment of a variety of health conditions [1]. The flowering tops of the plant are used to make teas, liquid extracts, capsules, or tablets sold as dietary supplements. A phytochemical investigation to explore the unknown constituents in the flowers of C. nobile led us to isolate and identify an 8-carbon keto saccharide acid and six of its derivatives. The structure of this 8-carbon sugar backbone was elucidated as β-3-deoxy-L-manno-2-octulopyranosonic acid, and its absolute structural configuration was completely assigned using 1D and 2D NMR techniques. This 8-carbon L-sugar skeleton has never been reported or isolated from a natural source. More interestingly, its D-isomer, namely 2-keto-3-deoxy-D-manno-octulosonic acid (KDO), is an essential component of the outer-cell membrane lipopolysaccharide (LPS) of gram-negative bacteria and plays critical roles in the biological system [2]. Inhibitors of KDO biosynthesis have the potential to be a new class of antibacterial agents [3].

Acknowledgements: This work was supported in part by “Science Based Authentication of Dietary Supplements”funded by the Food and Drug Administration grant No. 5U01FD004246, and the United States Department of Agriculture, Agricultural Research Service, Specific Cooperative Agreement No. 58 – 6408 – 02 – 1-612. References: [1] Simonetti G (1990) Stanley Schuler. ed. Simon & Schuster's Guide to Herbs and Spices. Simon & Schuster, Inc. ISBN 0 – 671 – 73489-X. [2] Cipolla L, Gabrielli L, et al. (2010) Nat Prod Rep, 27: 1618 – 1629. [3] Winzar R, Philips J, Kiefel MJ (2010) Synlett, 4: 583 – 586.