Four decades of structure determination by mass spectrometry: from alkaloids to heparin.

The early (1950's and 1960's) use of mass spectrometry in natural products chemistry and its evolution to the present significance in biochemistry is recounted. This methodology allowed the facile and speedy determination of the structure of a number of indole alkaloids, such as sarpagine, quebrachamine, and two groups isolated from the roots of Aspidosperma quebracho blanco. At the same time, the first strategy for the sequencing of small peptides by mass spectrometry was demonstrated. It slowly advanced, over a period of two decades, to an important alternative of the ubiquitous automated Edman degradation. Further advances in methodology and instrumentation established mass spectrometry as today's indispensable tool for the characterization of proteins in biochemistry and biology. A new concept of the ionization of highly acidic compounds as the protonated complexes with basic peptides, which allows the accurate determination of the molecular weights of the former, a highly sensitive method for the sequencing of heparin fragments and related sulfated glycosaminoglycans was developed more recently.