Biological and Phytochemical Screening of Plants

Saponins are a diverse group of compounds widely distributed in the plant kingdom, which are characterized by their structure containing a triterpene or steroid aglycone and one or more sugar chains. Consumer demand for natural products coupled with their physicochemical (surfactant) properties and mounting evidence on their biological activity (such as anticancer and anticholesterol activity) has led to the emergence of saponins as commercially significant compounds with expanding applications in food, cosmetics, and pharmaceutical sectors. The realization of their full commercial potential requires development of new processes/processing strategies to address the processing challenges posed by their complex nature. This review provides an update on the sources, properties, and applications of saponins with special focus on their extraction and purification. Also reviewed is the recent literature on the effect of processing on saponin structure/properties and the extraction and purification of sapogenins.

Saponins: Properties, Applications and Processing

Saponins occur widely in plant species and exhibit a range of biological properties, both beneficial and deleterious. This review, which covers the literature to mid 1986, is concerned with their occurrence in plants and their effects when consumed by animals and man. After a short discussion on the nature, occurrence, and biosynthesis of saponins, during which the distinction between steroidal and triterpenoid saponins is made, the structures of saponins which have been identified in a variety of plants used as human foods, animal feedingstuffs, herbs, and flavorings are described. Many of these compounds have been characterized only during the last 2 decades, and modern techniques of isolation, purification, and structural elucidation are discussed. Particular consideration is given to mild chemical and enzymatic methods of hydrolysis and to recent developments in the application of NMR and soft ionization MS techniques to structural elucidation. Methods currently used for the quantitative analysis of saponins, sapogenols, and glycoalkaloids are critically considered; advances in the use of newer methods being emphasized. The levels of saponins in a variety of foods and food plants are discussed in the context of the methods used and factors affecting these levels, including genetic origin, agronomic, and processing variables, are indicated. Critical consideration is given to the biological effects of saponins in food which are very varied and dependent upon both the amount and chemical structure of the individual compounds. The properties considered include membranolytic effects, toxic and fungitoxic effects, adverse effects on animal growth and performance, and the important hypocholesterolemic effect. A final section deals briefly with the pharmacological effects of saponins from ginseng, since use of this plant is increasing in certain sections of western society as well as being traditional in the Orient.

The chemistry and biological significance of saponins in foods and feedingstuffs.

The sex pheromone olean, found in the olive fruitfly, has the interesting property that one mirror-image variant attracts males and the other females. Olean contains as its only source of chirality a spiroacetal, a natural product consisting of an acetal (a molecule that contains two oxygencarbon single bonds at the same carbon atom) joining two rings. Until now chemists have not been able to mimic the enzymatic feat of synthesizing this type of chiral acetal centre, but this paper reports the design and synthesis of new chiral acids that can catalyse selective spiroacetalizations, including one to furnish olean with remarkably high selectivity. A distinctive characteristic of these artificial catalysts is an extremely tight chiral pocket, reminiscent of those found in natural enzymes.

Asymmetric spiroacetalization catalysed by confined Brønsted acids

Camptothecin and taxol are secondary metabolites found, respectively, in the wood bark of Camptotheca acuminata , a native of China, and Taxus brevifolia , found in the northwest Pacific coastal region of the United States. The compounds were isolated guided by bioassay on various extracts and chromatographic fractions. Their unique and hitherto unknown structures were elucidated by nuclear magnetic resonance, mass spectrometry, and X-ray analysis. Both compounds have unique mechanisms of antitumor activity; camptothecin uniquely inhibits an enzyme, topoisomerase I, involved in DNA replication. Taxol binds to a protein, tubulin, thus inhibiting cell division. Taxol has been called the best new anticancer agent developed from natural products, showing particular efficacy against ovarian cancer. Camptothecin and analogues singly or combined with cisplatin show efficacy against solid tumors, breast, lung, and colorectal, which hitherto have been unaffected by most cancer chemotherapeutic agents.

https://cancerres.aacrjournals.org/content/canres/55/4/753.full.pdf

Camptothecin and Taxol: Discovery to Clinic—Thirteenth Bruce F. Cain Memorial Award Lecture

This is a report of the chemical examination of the fourth 1,000 accessions in a survey of plants for steroidal sapogenins and is thus a continuation of the reports on the first three 1,000 accessions (1-6). Data are given for 950 samples, representing 100 families, 272 genera, and 432 identified species. Of these, 14 families, 151 genera, and 376 species are new in this series. Quantitative data are given for the occurrence of 15 steroidal sapogenins, of which two, gentrogenin and correllogenin, are new. Qualitative data are given for the occurrence of these groups of constituents: saponins, flavonoids, alkaloids, tannins, and unsaturated sterols. There is no previously published chemical information on about 50 per cent of the species examined.

Monroe E. Wall

Papers

Steroidal sapogenins. XXV. Survey of plants for steroidal sapogenins and other constituents.

Steroidal sapogenins i. extraction, isolation, and identification

Steroidal Sapogenins. XXVIII.2 Conversion of Steroidal Sapogenins to Δ16-20-Keto-pregnenes3

Scientific EditionSteroidal Sapogenins XLIII. Survey of Plants for Steroidal Sapogenins and Other Constituents

Steroidal Sapogenins. XXVII. Preparation and Properties of 20-Isosapogenins2