Dear Vallabh, as you would very well know that any herbal medicine or a part of herb used as a cure has many different constituents. Some of these may be responsible for the therapeutic action of the drug, while others may be useless. Infact, many compounds may together result in a single action. In order to pinpoint a single active constituent extensive lab testing is required. This was the way many of the drugs we use today, were discovered. We can absolutely isolate and characterize the compound...but it is an lengthy and exhaustive process, Their is no single standard procedure..you will have to do many lab tests....The info is easily available on internet.

Thanks Dr. Sudarshan

My question is still there whether it single constituents or collective which constituents  responsible to cure the disease or use in cosmetics .I had extracted Aloe vera gel and it contains biological active compounds like acemanan manose, galactose  etc. but which compound responsible for particular is still mystry or research is going on?

Activity-guided fractionation is the method employed to identify biologically active compounds. Compounds in fractiions collected from column chromatography are tested in biological systems. However, this is a laborious and expensive method.

Thanks Punit and Dr.Suresh

I think an unexploited plant directly used as Ayurveda medicine but to characterize and extract a single compound is step by step process. We can not directly know the what the compounds contains in sample.

This is a very important question, and research is still ongoing in identifying the compounds that are crucial to the beneficial effects of a plant. As mentioned in the discussion, the accurate methods to identify these compounds are long processes, relying on targeted isolation of the metabolites in the tissue of the plant and testing them individually. This has been demonstrated to work and indeed many medicinal molecules have been identified this way. However, I would argue that Ayurvedic medicine emphasizes balance of the doshas, and that focusing on the single compound that is most important to the beneficial effect of a plant or tincture may not provide the same benefit when taken alone, as when prepared with the other compounds present in the plant with that specific molecule. By isolating these compounds, you may lose the additive (or even greater) effects of all compounds working together. I am not suggesting it is not a good idea to try to decipher from the wide array of compounds which are beneficial, but I think there is an argument to be made that many of our modern methods for purification will reduce the system to individual components that on their own contribute little to the symptom they are treating, and the community will gain little from having purified compounds as opposed to how they are currently produced. To gain greater insight, perhaps look at commonly used plants in Ayurvedic medicine and see if you can find common groups of metabolites. This can also be expanded outside of Ayurveda, and look at the plants identified for medicinal use by ethnobotanists around the world. You may find that the presence of enzyme families in these species are common to those in Ayurvedic practice that have the same effect when used (e.g. plants from the Lamiaceae (basil, mint) family are used in Europe and southern Asia) and could help suggest targets for identification. However, you may need to combine many of these compounds to find a mixture that has similar effects to the traditionally processed plant material. This is also why in the US, regulatory agencies have a hard time allowing herbal supplement companies to make claims about health benefits directly on their product, since in laboratory testing does not often conclusively show many of the benefits associated with the plants that these compounds are derived from, due to the nature of the processing. Instead, companies choose to make whole tissue extracts, or ground tissues in capsules, without specifying what in the mix is directly providing the benefit.

An example of work done to identify the important compounds in Neem is presented here: http://www.sciencedirect.com/science/article/pii/S1658365513000423

and a good discussion of how to extract compounds is here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3218439/

Great question and there is no real yes or no answer. You can separate the compounds with all menthods mentionned above but you would need a way of checking what each compound does to a or multiple cells lines to prove function i.r brain stem cells of rat or skin/muscle cell line.

There is a thin line between the efficacy of the drug and presence of compounds in the drug.It is not necessary that of the compound is isolated it will work on certain disorder,sometimes it may work  but majorly it is otherwise.The herbal drug according to Ayurveda acts as a whole and not as an isolated compound.There must be these catalytic compounds which facilitate the action of the active compound.That is they work synergistically.Sometimes a single drug may also not work ,then polyherbal formulations have been made for the same reason. 

Thanks a lot  Johan Jaenisch for giving thorough understanding of the issue.

Also thanks to Machael and Jyoti for sharing their knowledge.

TO DETERMINE THE ACTIVE COMPOUND YOU SHOULD DO INVITO ASSAY 

Dear Sir, Please see the published article  http://www.greenpharmacy.info/index.php/ijgp/article/view/577

This is not absolute answer of your question but it may help