ESI-MS/MS of Natural Products Database Project

Introduction

Throughout the history, natural products have been used as medicines and remedies for the treatment of various diseases. Approximately 175,000 known structures have been reported. Undoubtedly, natural products have a great chemical diversity, this makes them a considerable source of potential drug leads [1]. Many of the drugs discovered in the last three decades either belong to the natural products or are derived from the natural products [2-4]. The biological activities of discovered natural products are very diverse and include anti-inflammatory, antibacterial, antiviral, antiulcer, anticancer and other type of activities. A recently reported data of all approved drugs from natural products and other sources covering all countries/diseases during the time frame of 1981-2010 indicates that 48.6% of small drug molecules were either natural products or their derivatives [5]. Moreover, about 80% of the world population depends on herbal medication and the yearly sale of herbal medicines and homeopathic remedies is larger than US $45 billion in US alone [6].
At the same time the isolation, identification and analyses for quality control purposes of natural products holds promised and prospects. It also poses a problem to scientific research in being time consuming and often cumbersome. There have been many advances in the past for the isolation and analyses of natural products like the use of powerful extraction and chromatographic techniques [7]. Recent advances include the use of hyphenated techniques like gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS) and more advanced techniques like LC-NMR-MS [8]. These techniques allow the analyses of natural products mixture prior to isolation to make sure that the mixture contains a compound of interest.
The use of electrospray tandem mass spectrometric (ESI-MS/MS) techniques offers the analyses of a wide range of compounds using miniscule amounts of samples due to the enhanced sensitivity of mass spectrometers. Special features of this mass spectrometry technique includes.

• Ability to observe a diverse number of molecular species ranging from small molecular weight compounds to large molecular weight compounds like proteins.
• Highly soft ionization techniques ionize the compound without any breakage.
• Tendem mass spectrometry feature utilize the cleavage of compounds in a controlled manner which provides very useful structural information.
• Offers a dynamic range of concentration.
• Reproducible qualitative/quantitative analyses.
• This technique has been coupled with the most advanced liquid chromatographic (LC) techniques like HPLC or UPLC. The coupled systems like HPLC-ESI-MS/MS are widely available from various manufacturers and are being used for various purposes.

Due to the aforementioned advantages, this technique has been used extensively for the analyses of many natural products [9-12]. Moreover ESI-MS/MS techniques coupled with chromatography have been successfully employed for simultaneous analyses of various compounds of natural origin [9-13], food samples [14], drugs [15-22], compounds of forensic importance [16, 17, 23] and environmental samples [24].