Frontiers in Natural Product Chemistry

Cancer is a serious public health problem that affects both men and women. Globally cancer is one of the leading causes of death. The risk factors associated with cancer development are categorized into intrinsic and extrinsic. The treatment modalities used in the treatment of cancer, such as chemotherapy, radiotherapy, surgery, and targeted therapies have adverse effects either during or after therapy. Currently, plant-derived anticancer compounds are being used in the treatment of various cancers. The variation of these compounds is according to their origin, general classification, and mechanism of action. Various studies have shown that anticancer agents of natural origin have fewer side effects when compared to traditional therapies. Anticancer agents of natural origins are a revolution in the field of cancer research and treatment as they are easy to isolate, cost-effective, and reliable to use. The advantage of anticancer agents of natural origin over synthetic ones and conventional therapeutic options is that their functions are selective and specific to a tumor undergoing treatment. This article is aimed at covering the success of plant-derived anticancer agents in the treatment of cancer, as well as their mechanism of action and the limitations associated with current therapeutic options.

The family of benanomicin-pradimicin antibiotics (BPAs) is reviewed exhaustively with respect to its structural, functional, mechanistic and synthetic aspects. BPAs can be considered a unique class of compounds from the structural point of view due to the presence of a 5,6-dihydro-benzo[α]naphthacenequinone (DHBNQ) scaffold attached to a glycan moiety. The mechanism of action is ‘lectin-like’ and related to the selective recognition and binding to specific mannoside residues located at the surface of the membrane of fungal and viral pathogens. BPAs are prototype structures of non-peptidic small-size carbohydrate-binding agents (CBAs).

For many years, natural products have been exploited to obtain extracts and pure substances, especially to treat various diseases and conditions. Bixa orellana, the seasoning and colouring known as “Achiote”, is used in several countries in traditional medicine to treat a variety of health needs, mainly using the dried pulp of the fruit, the seeds, the leaves and the roots. The objective of this review is to provide information regarding the numerous pharmacological activities of the different parts and extracts of B. orellana, such as the anti-inflammatory, anti-bacterial and anti-parasitic activity, as well as the hypoglycaemic, cytotoxic, antioxidant, bronchodilator, diuretic and hepatoprotective effects. This information will promote the development of further research regarding this plant and its various benefits, either in the form of an extract or pure substance, such as bixin and norbixin. Similarly, it will allow the discovery of its various mechanisms of action for each disease, which will promote the development of new active compounds.

Human beings from prehistoric period are mainly dependent on mother nature for the fulfilment of their elementary needs, such as medicines, foodstuffs, shelters, clothing, flavors and fragrances, etc. From ancient times, medicinal plants are known to act as a source of a variety therapeutic agents which are widely used in traditional medicine system to cure the various deteriorative diseases and ailments. The wide range of therapeutic applications of various medicinal plants is largely attributed to the presence of a variety of bioactive secondary metabolites (SMs), such as alkaloids, terpenoids, steroids, flavonoids, polyphenolic acids, saponins, tannins, glycosides and essential oils etc. Apart from a variety of traditional uses, medicinal plants are also well known for their notable pharmacological potential like anticancer, antiperiodic, antimicrobial, analgesic, antiemetic, antitumor, antioxidant, antiinflammatory, antiarthritic, etc. Ajuga bracteosa Wall. ex Benth (A. bracteosa), commonly known as Nilakanthi in Ayurveda belongs to the family Lamiaceae, is an important endangered medicinal plant of Himalayan origin. A. bracteosa is a good source of flavanol, glycosides, ergosterol, neo-clerodane diterpenoids, iridoid glycosides, 8-endoperoxide and phyto-ecdysones, which shows numerous biological and pharmacological activities viz. antiviral, antitumor, antimicrobial, antiplasmodial, anti-inflammatory, antiarthritic, antioxidant, etc. Further, variety of A. bracteosa leaves uses had been elaborately described in Ayurveda, Unani and Chinese medicine text, for the treatment of numerous ailments like agues, dysentery, vomiting etc. The plant is also known for its antivenom potential against snake bite. A. bracteosa is an endangered and medicinally high valued Himalayan species that why it is very significant to reveal its full potency. Therefore, the present article mainly focuses on the distribution, cultivation, traditional uses, phytochemistry, pharmacological potential and future prospective of this versatile Himalayan plant.

Tetracyclic benzocarbazoles are examples of nitrogen-containing heterocycles, which display interesting pharmacological activities and physicochemical properties. This chapter aims to bring some examples about the synthesis of bezocarbazoles, mostly benzo[a]carbazoles (including the dihydro and tetrahydro derivatives), with interesting properties. This chapter also includes aza-pterocarpans and aza-coumestans, which are structurally similar to benzo [a] carbazoles, although their analogous natural products are formed through different biosynthetic pathways. Being aware of the potential interest of these compounds, many efforts have been made for the development of new methodologies to carry out their synthesis and will be discussed below.

Flavonoids are naturally sourced compounds found in many substances consumed as food and have beneficial effects on human health. Chalcones, essential members of the flavonoid family, have also attracted many researchers' attention due to their wide range of pharmacological effects. In this chapter, the antiinflammatory, antidiabetic, and antidepressant activities of the natural compounds in the structure of chalcones and the compounds synthesized with the help these compounds will be discussed. It has been written after a literature review of the articles published between 2000 and 2020 and aims to be a guide for designing new active drug ingredients.

Natural products have played a key role in cancer drug discovery, as well in other therapeutic fields. In the past decades, marine organisms have proven to be a primary source of new potentially bioactive natural products for drug discovery. By reviewing the literature describing marine organisms and isolated metabolites, we can notice a large increase in the number of studies today compared to the end of the 20th century. The number of structures isolated each year has almost doubled over the past 20 years. Because of their topicality, we have focused on natural bioactive steroids isolated from marine organisms. In the chapter ‘Bioactive Steroids from Marine Organisms’, an overview of the new steroid compounds isolated from marine sponges, macroalgae and cucumbers, described in the relevant literature in the period from 2011 to 2020, is given. To provide a comprehensive introduction in the field of marine bioactive steroids, we highlighted typical molecules grouped according to their structural characteristics with additional reference to their biological activity. The structures of the new compounds, their natural origin (species of the organism) and their rich biological activities are presented and described in detail. In addition, biological tests performed on known compounds during this time period are also described. Some of the compounds possess multiple activities and have been tested only in a limited number of biological assays, which means that the full potential and significance of these compounds may only be discovered in the future.