Nepal Academy of Science and Technology (NAST)

Science & Technology for National Development

Natural Products Chemistry

Sajan Lal Shyaula,  PhD
Coordinator

Tel:+977-1-5547715 (Ext: 269; 270; 273)
E. mail- sajan.shyaula@nast.gov.np 

 

Isolation and characterization of natural constituents

With the help of the experiences gained by the people through many generations, the traditional medicinal practitioners, faith healers and ethnic groups have made use of herbal products for various purposes. The herbal plants are being consumed by the people for the treatment of infectious diseases like flu, measles, typhoid, diarrhea, wound, cold, cough and other microbial diseases. Many medicinal plants such as Aconitum species, Aconitum spicatum, Acorus calamus, Allium prattii, Bergenia ciliate, Bergenia purpurascens, Caragana jubata, Caragana sukiensis, Mallotus philippensis, Picrorhiza scrophulariaeflora, Rheum australe, Rheum nobile, Rhododendron anthopogon, Usnea aciculifera, Zanthoxylum armatum and many more are currently under chemical and biological investigation in our laboratories. As depicted in the left figure, three C-19 norditerpenoid alkaloids were isolated from the tubers of Aconitum spicatum and their antileshmanial activity was reported. Our works on natural products together with others have been described in several review articles.

Quantitative, qualitative and biological evaluation of natural products

We perform standardization of plant materials and plant products through various physicochemical parameters, chemical tests and instrumental analyses. We evaluate the biological properties of the plant extracts and natural constituents isolated through various in vitro and in vivo biological assays such as antimicrobial susceptibility assay, anti-fungal assays, brine-shrimp lethality assay, antioxidant capacity assays, enzyme inhibition studies, assays on animal models, etc. Figure on left side shows HPLC fingerprinting analysis of the rhizome extract of the Himalayan rhubarb Rheum nobile that constituted anthraquinones (chrysophanol, emodin and physcion). A graph presented below indicates antidiabetic activity of the same plant material in rat models.

Essential oils

Essential oils obtained by hydrodistillation and simultaneous distillation of various plants’ parts and spices are evaluated for the quality using GC-MS analysis and other analytical methods. We aim to standardize our essential oil products for the global market.

 

Biotrasformation of secondary metabolites

Medicinal plants mostly contain active secondary metabolites; have diverse physiological and pharmacological activities. Secondary metabolites show potent activities against the organisms and exhibit anititumor, antiallergic, anti-inflammatory, etc. properties. Selective functionalization by chemical methods at unactivated carbon atoms has been a major challenge in organic synthesis, and thus microbiological methods have frequently been used for this purpose. Biotransformations involve the use of enzymes or microorganisms to perform chemical reactions in which the starting substances and products are of comparable chemical complexity. On our studies, the secondary metabolites isolated from the medicinal plants, which showed the biological activities, are subjected for the biotransformation, and transformed products are purified and identified by spectroscopic analyses. Thus obtained transformed compounds are further screened for the biological activities.

 

Derivatisation of natural bioactive compounds for activity enhancement

We are working on derivatisation of natural secondary metabolites such as flavonoids and anthraquinones for enhancement of their bioactivities. For example, quercetin, a naturally occurring flavonoid, exhibits a high antioxidative property. Unfortunately its water insoluble property and the nature of rapid conjugation with glucuronosyltransferases and sulfotransferases present in the small intestine halts it to reach in the malignant organs through gastrointestinal tract in oral therapy. We have prepared several quercetin derivatives and compared their antioxidative property using the DPPH free radical scavenging assay. We also rationale the result obtained through the molecular calculations.

Development of novel synthetic methodologies

Development of novel strategies for the synthesis of various target molecules is our another research topic. We have established all basic requirements to work on advanced organic synthesis. Currently we are using various metal (Cu, Ag, Au, Fe, Ru, Rh, Ni, Pd, Pt, etc.) complexes to develop new catalytic reactions and studying their mechanisms. Cyclizations, nucleophilic additions, C-H activations and macrolide synthesis are our currently running projects. We achieved a landmark international publication on organic synthesis working solely in the country.

Development of industrial processes and green chemistry

We are focusing on development of economic, industrial processes. Avoiding of organic solvents and hazardous reagents, development of high yielding and atom economic process, the use of mild conditions and ease work up protocols, microwave synthesis and short step total synthesis are the goals. Our achievements can be read in research articles and patents in the near future. 

 

Analytical services

We provide analytical services to our customers from the government, private and academic institutions under nominal charges and mutual collaborations. We are equipped with HPLC, MPLC, GC-MS, LC-MS, FT-IR, UV, XRD, AAS, CHN analyzer, Glove box, Elisa reader, etc. Following facilities currently exist in our laboratories.