Literature Review
2.1. Introduction
Plant-based medicine is the principal source of the drug in different traditional medicinal system that has been passed orally from generation to generation. The World Health Organization (WHO) has estimated that over 65% of the world's population still depends on the plant product as curative agent to improve the health (Cragg et al., 2009). In Europe and North America, the knowledge of traditional healing system has led to an increasing interest in herbal medicine (Tyler, 2000). These herbal medicine has been incorporated into so-called „alternative,‟ „complementary,‟ „holistic‟ medical system and also called as „phytomedicine‟. In India, about 70% of the modern drugs are from natural resources, and many synthetic analogs have been prepared from the prototype inspired from the plant (Sen et al., 2011; Pan et al., 2014).
Advancement in chemical analysis has allowed researchers to extract and modify active ingredients from plants. The efficacy and effectiveness of these products have been demonstrated using modern technological and scientific tools which have aided in the treatment of various acute and chronic infectious diseases. Therefore, the search for novel therapeutic agent continues for an effective medication for treating/curing deadly diseases either by direct therapeutic effect after semisynthetic modification or by new synthesis of chemicals based on the natural product model. Natural products from medicinal plants are hub of structurally diverse array of pharmacologically active compounds that have proved to be indispensable for the cure of deadly diseases or as lead structure for novel pharmaceuticals (Newmann et al., 2000).
Chapter 2|6 2.2. History of herbal medicine
History of medicine dates back practically to the existence of human civilization. Human has always been dependent on the natural resources especially plants for their primary healthcare. This knowledge of herbal medicine for curing ailments or disease has been passed orally through generations. Historically, majority of new drugs have been synthesized or inspired by natural products due to their excellent chemical scaffold.
One of the earliest record of medical documents „Papyrus Ebers‟ wrote by Egyptians around 1500 BC, documented around 700 plant-based remedies (Table 2.1).
A similar record of herbal study „Shennong Bencaojing‟ was written by the Chinese Emperor Shen Nong around 2000 BC, contains information about 300 plants.
Before the 20th century, crude extract of plants, animals, and minerals represented the only medication available to treat human and domestic animal illness. With advancement in the field of chemistry, plants were intensively examined for their utility aspect as it relates to medicines (Phillipson, 2001). In 1804, „morphine‟ was purified from opium by Serturner and found that it has analgesic and sedative effects (Lockemann and Serturner, 1951). After this discovery, other scientists started to seek “active principles” of medicinal plants. Two French scientists, Caventou and Pelletier isolated quinine from Cinchona bark or Peruvian bark in 1820 and made a notable breakthrough in the history of herbal medicine (Borchardt, 1996). Subsequent years later, scientists discovered narcotine (1817), caffeine (1821) and atropine (1831).
Chapter 2|7 Table 2.1 History of natural product medicine (Source: Sarkar et al., 2006).
Period Type Description
>3000 BC Ayurveda Chinese Traditional Medicine
Introduced medicinal properties of plant and other natural products
1550 BC Ebers Papyrus Present a large number of crude drug from natural sources (e.g., castor seeds and gum Arabic) 460-377 BC Hippocrates Describe several plants and animals that can be the
source of medicine
370-287 BC Theophrastus Describe several plants and animals that can be the source of medicine
23-79 AD Pliny the Elder Describe several plants and animals that can be the source of medicine
60-80 AD Dioscorides Describe several plants and animals that can be the source of medicine
131-200 AD Galen Practiced botanical medicine (Galenicals) and made them popular in the west
15th Century Krauterbuch Presented information and pictures of medicinal plants
The structural elucidation and characterization of natural products geared up after morphine structure was determined in 1923 (Gulland and Robinson, 1923), quinine's structure in 1908 (Rabe, 1908) and cocaine in 1898 (Willstatter and Muller, 1898). In 1956, morphine was first synthesized by Gates and Tschudi and encouraged other scientist towards the synthesis of natural products (Gates and Tschudi, 1956). The 20th century has revolutionized entirely the idea of using the extracts as drug and target mediated by specific interactions with biological macromolecules. It has led the scientists to conclude that individual active compound in extract are responsible for biological activity of the drug (Lahlou, 2013). This concept eventually led to the beginning of a new era in pharmacology that is to use the pure isolated chemical towards treatment of diseases.
Several plant-based natural products have been isolated after the onset of World War II and are found to be promising till date. Few notable were the discovery of „reserpine‟
from Rauwolfia serpentina roots (used as a potent tranquilizer), anticancer drug
Chapter 2|8
„vinblastin‟ and „vincristine‟ from Catharanthus roseus (Phillipsons, 2001). Other remarkable achievements were the discovery of „Camptothecin‟ and „Taxol‟ which are regarded as lifesaving drugs in cancer therapy (Oberlies and Kroll, 2004). Many natural products and their derivatives are still in use to combat various infectious and non- infectious diseases and are regarded as potent antibacterial, anticancerous agents (Butler, 2008; Newman and Cragg, 2012).