Purification of Water-Soluble Natural Products

Recent advancement in separation and structure elucidation methods has been remarkable. It is not unusual for submicrograms of substances to be purified from vast amounts of biological material and their structures elucidated. The major contributing factors are progress in high-performance chromatography technique and computer-aided high-resolution nuclear magnetic resonance (NMR). With the help of these two techniques, a number of minute biologically important substances have been brought to light, which would have been inconceivable a few decades ago. Despite all this, the purification of small water-soluble molecules is still shunned by most researchers. For example, a glance at the natural products section of Chemical Abstracts shows that about 95% of new substances reported are in the lipid-soluble category. There may be more lipid-soluble compounds than water-soluble compounds in nature, but this ratio seems to be greatly disproportionate. Clearly, this reflects the difficulty in purifying small-molecular-weight water-soluble compounds. About 10 yr ago, this author wrote a guide for the purification of marine natural products with an emphasis on the water-soluble compounds (1 ). This chapter is intended to present an updated general procedure with new specific examples.