Dear Anas: Markus Ganzera sent to you a precise advice about your question, either if you know or you don't know the active ingredient. Try to follow them.

If you are interested by untargeted classes of natural products which fit with pharmacological requirements (in terms of logP, MW etc...) and from a wide range of plant families, I observed that several labs are using ethyl acetate crude extracts (with SPE on polyamide prior to biological evaluation); Then a LC-HRMS short run correlated with a database seems to be more and more efficient for dereplication of these extracts. But if you want to study the composition of a special medicinal plant I would suggest to perform successive extractions with 3-4 solvents polarity (from hexane or petroleum ether to methanol or even water) and a bioguided separation as proposed by Markus Ganzera.

At first, look for your plant in the scientific journals, may there are previous report about it.

I am also working partially on isolation of active ingredients from medicinal plants.

1st we depend on literature. if it confirms some active classes, e.g alkaloids etc, then we use specific procedures in literature and isolate them, followed by their derivatization and pharmacological evaluation.

2nd if plant is new and not initially investigated, then we study genera and family of that plant, and from that we have to decide about our work.

while generally the researchers get an ethanolic extract of the plant, do fractionation, and perform different tests for the classes of different compounds. then they get idea and decide to carry research on the whole or one fraction.

best of luck

The most common extraction solvents are ethanol and water. Either as pure solvents or in combination, in various concentrations.

Very roughly: Ethanol extracts;  alkaloids, resins balsams ether oils. Water extracts; glycosides, saponins, bitters, sugars. Modern extraction often performed with supercritical CO2.

But just as important as choice of extraction solvent is the choice of method of extraction. Simple maceration or continues percolation.

There are excellent databases such as NAPRALERT, Dr. Duke's etc. which provide detailed information on plant species, their composition and biological activities of the compounds. Based on this information, you can proceed further for isolation of specific compounds present in your test species.

I agree with Marqus Ganzera

You can extract your medicinal plant sample suspected to contain bioactives in solvents of different polarity such as chloroform ,water,hexane,methanol,ethyl acetate and ethanol. You can further conduct chromatograhy(TLC) om each of the crude to observe which among gives you more  constituents. Then perform phytochemical screening to observe which gave u positive for your target phytochemicals.after you can then proceed with the isolation of the constitutents.

 Thanks

You can extract the medicinal plant compounds using solvents in order of increasing or decreasing polarity, depending on the type of compounds you want to isolate. For example, if you start with hexane, first you will extract fat ... etc.

In respect about flavonoids non glycosilated, you can use Hexane-Bencene-ethyl acetate-ethanol.

I am specific to the second part of question- how are they to know the active ingredient in the medical plant? In this regard the clue may be obtained from all traditional sciences and ethnic botanical knowledge.

For a Natural product researcher its not so difficult to understand the active ingredients of medicinal plants. Previous information and of course ethnic knowledge both can give you lots of information . Also get information from NAPRALERT. It is believed plants produce many chemicals which are biologically very active. Following link can give some clue: www.medicinalplants-pharmacognosy.com/...s-topics 

Pharmacoergasy

Collection of Herbs

Conservation of medicinal plants

If follow the heritage herbal knowledge, which is in practice since many centuries will be definitely much more value added information, which is not explored from huge herbal treasure.

Since your interest lies with natural products, these publications may be helpful to you.

Some more publications for your information.

Dear Dr B.R. Rajeswara Rao

what is the difference between medicinal plants and Aromatic plant 

Dear Dr. Hend Maarf

Medicinal plants are the pants which contain phytochemicals that used to manage or treat the diseases while aromatic plants are the plants which contain aromatic phytochemicals that used in perfume manufacturing. A plant may have both properties, single or not.