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Natural product isolation

There has been a remarkable resurgence of interest in natural product research over the last decade or so.

With the outstanding developments in the areas of separation science, spectroscopic techniques, and microplate-based ultrasensitive in vitro assays, natural product research is enjoying renewed attention for providing novel and interesting chemical scaffolds.

The various available hyphenated techniques, e.g., GC-MS, LC-PDA, LC-MS, LC-FTIR, LC-NMR, LC-NMR-MS, CE-MS, have made possible the preisolation analyses of crude extracts or fractions from different natural sources, isolation and on-line detection of natural products, chemotaxonomic studies, chemical finger printing, quality control of herbal products, dereplication of natural products, and metabolomic studies.

While different chapters in this book are devoted to a number of specific aspects of natural product isolation protocols, this chapter presents, with practical examples, a general overview of the processes involved in natural product research, starting from extraction to determination of the structures of purified products and their biological activity.

Natural products, well known for unique chemical diversity and bioactivity, have continued to offer templates for the development of novel scaffolds of drugs.

With the remarkable developments in the areas of separation science, spectroscopic techniques, microplate-based ultrasensitive in vitro assays and high-throughput screening (HTS) technologies, natural products research has gained momentum in recent years.

The pre-isolation analyses of crude extracts or fraction from different natural matrices, isolation, online detection and dereplication of natural products, studies on chemotaxonomy and biosynthesis, chemical finger-printing, quality control of herbal products, and metabolomic studies have now become much easier than ever before because of the availability of a number of modern sophisticated hyphenated techniques, e.g., GC-MS, LC-PDA, LC-MS, LC-FTIR, LC-NMR, LC-NMR-MS, and CE-MS.

This introductory chapter presents a general overview of the processes involved in natural products research, starting from extraction and isolation to elucidation of the structures of purified natural products and their bioactivity.

Isolation of natural product

The basic principles of natural products isolation have not changed much in the last 50 years.

However, new chromatographic methods have been developed and recently, conventional column chromatography has evolved to fl exible high-throughput gradient fl ash and medium pressure liquid chromatography allowing an hour separation of a kilogram to milligram levels of crude extract and fractions (see Chapter 7).

Such systems elute compounds at a remarkably reproducible retention time. In phytochemistry, the same plants or species are still being investigated.

Many plants that seem uninvestigated may have names that are synonyms and thus could have been studied. This has made the isolation of new compounds or novel moieties or natural drug molecules a rare feat.

However, reinvestigation of known or well-studied plants has also yielded new compounds. This is possible with the emergence of high-throughput chromatography, where loading capabilities can be increased to 100 g levels.

Dereplication techniques have also greatly advanced by the introduction of high-resolution GC–MS, LC-MS, MALDI, MS/MS, and metabolomic studies.

A boost has been given to structure elucidation through high-fi eld NMR instruments and two-dimensional NMR techniques capable of probing any structural relationship in a compound.

Isolation of pure compounds from their crude extracts requires more ingenuity.

Since most plants commonly used in traditional medicine or as herbs and spices have been investigated, it is very likely that the abundant major components from their extracts have been earlier reported.

It has become a more diffi cult to isolate the scarcer novel minor secondary metabolites.

This is compounded by the fact that the minor components are derivatives of the abundant ones and may not be easy to chromatographically separate.

However, nowadays this has become imperative as it is the norm to screen pure compounds rather than crude extracts or fractions.

Screening of crude extracts or fractions does not allow understanding of the mode of activity of the test compounds against the target cells or tissues.

It also does not permit working out the minimum active molar concentrations of the “hit” compound(s) even when their presence in the mixture can be quantifi ed.

Unless spectroscopic studies and physical properties indicate that a compound is pure, they cannot be put forward as a lead compound.

In modern drug discovery programs, complete identifi cation and structure elucidation of the biologically active natural product is obligatory.

Natural product isolation techniques

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Normally, we do not publish such types of papers as case study, technical note or meta-aThere has been a remarkable resurgence of interest in natural product research over the last decade or so.

With the outstanding developments in the areas of separation science, spectroscopic techniques, and microplate-based ultrasensitive in vitro assays, natural product research is enjoying renewed attention for providing novel and interesting chemical scaffolds.

The various available hyphenated techniques, e.g., GC-MS, LC-PDA, LC-MS, LC-FTIR, LC-NMR, LC-NMR-MS, CE-MS, have made possible the pre-isolation analyses of crude extracts or fractions from different natural sources, isolation and on-line detection of natural products, chemotaxonomic studies, chemical fingerprinting, quality control of herbal products, dereplication of natural products, and metabolomic studies.

While different chapters in this book are devoted to a number of specific aspects of natural product isolation protocols, this chapter presents, with practical examples, a general overview of the processes involved in natural product research, starting from extraction to determination of the structures of purified products and their biological activity analysis unless the topic is of exceptionally significance and urgency.

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