The method depending on what you wish to isolate a single compound and identification you should use phytochemical. Or you looking for activities you should use crude extract first.

Hello,

In my opinion, if your plant crude extract having desired activity then you can go for isolation, identification of single compound and their related activity.

It is always significant if you report a single compound activity, but simultaneously u can report crude extract activity too. 

Single compound activity or study is having more importance, because a single compound can be ready to think about apply in therapeutics.

Good luck :)

Hi,in addition of nice comments above,  I think it will be also nicer, you can at first do metabolite profiling of your extracts or fractions of extracts by using LCMS or GC MS or other chromatography methods, and please do also some bio-activities studies of your extracts or fractions of the extracts. By using multivariate analysis PCA, PLS-DA, I think you can predict, which from your compounds (peaks in TIC of LCMS/GCMS) have certain bio-activities. After these experiments, you can decide which compounds should be isolated and further analysis. If you used LC MS, I think you can apply to HPLC preparative using DAD or other non destructive detectors to isolate your target compound(s). kind regards

If you are interested in the structure then -In addition to the above answer I would like to add that FTIR will help identify the functional groups of the phytochemical isolated.The exact structure of the isolated phytochemical can be identified by NMR spectroscopy.

If you are interested in the activity then you should select the extract ,it will display the different activities after bioassays.

Structure activity relations can be carried out after toxicity studies/animal experiments.

You can work with either or both depending on what you want achieve. Bioassays work better with crude extracts, and the isolates may not manifest the same results due to synergistic, promotional and antagonistic effects, all of which their ideal cut off points have no been well established 

Normally to find active principle you should  try with the extract and then try with the fractions and finally with the isolated compounds using the fractionte bioguide trying to follow the active fraction until the active principle.

Plant extracts will provide you the results in any of your study based on the synergetic activity of compounds present in it and the type of solvents used for the extraction. Hence, it is better to determine the active extract used in the study and go for the isolation and characterization of the compounds responsible for the activity or activities.

Good luck

@Stanley, it will be good to make your question more specific. The type of plant extract to use depends on your research question, specific objectives and outcome being looked out for. For cancer studies for example using  human cell line, pure extract of the herbal medicine, extracted using TLC and CC could be better than crude extracts. For phytochemical screening, biochemical,basic toxicity studies and characterization, crude extracts could be used.  For , So, your choice depends on research question and objectives as said earlier.

Good luck

The option depends on the objective of your research. The crude extracts or the isolated phytochemicals can be superior one over another in terms of activity.

it depends on the researchers and their targets, also depends on synergy .... if researcher wants to use nature to explore molecule as a lead, definitely he have to work on isolation, how ever the molecular mechanism is possible to establish only on isolated moieties... But in case of antipsychotics it's better to work on cure drugs best examples like Hypericum and passiflora

We can include evaluation of succulent plant parts or their extracts (Root, Stem, Bark, Leave etc. directly or the extracts taken out from them directly by pressure) of reported medicinal plants just after collection from the living plants as an additional parameter during planning any study for validation of their reported efficacy. This may create a new way in research, medicine development and industry. Modification of presently known analyzing procedures may be required for this.

Anybody can download a Power Point from my RG site with some more information.

Dr.S.Pattanayak,Kolkata, India.

always better to work with the plant extracts initially,. as the reports suggests the numerous chemical constituents will work synergistically for the activity. after satisfactory results with the extracts explore the chief constituent responsible for the action and isolate the compounds and confirm the activity

Dejar Stanley

Your question is not clear for me. It suppouses you make and extract and then you try to isolate the active phytochemicals trying the bioassays, through the  method called Isolation of the active principle through bioassays, it means you try the bioassays in the crude extract and then  you make the fractions and try the bioassays again, and so on until get the active compounds.

If you feel any answer is helpful to you, then recommend such answer/s.

Dear Stanley,

It depends on the objective of your research. as crude extract is combination of polyphenols/phytochemicals may have higher activity than isolated compound. where as Isolated compound will show activity of its own while crude extract will show activity of the whole extract which is multiple active compounds.

It's depend up on pharmacological synergy , safety and efficacy

Dear RG colleague

I think that before isolating and identifying a bioactive compound, we should study the extracts (crude, fractions). The active fraction will be then investigated for identifying the bioactive molecule.

Often, the identified molecules are known and their activity established. The challenge is to discover a new active molecule.

Best regards