I don't think you can effectively isolate syncytiotrophoblast - it all breaks up in the digestion process to get to the cytotrophs. You can use explants of placental villi, which retains the structure and morphology of the tissue, but obviously not the fetal vs maternal interface. The classic method for isolating cytotrophoblasts is by Kliman et al 1986, from where most other methods have been adapted:

http://press.endocrine.org/doi/abs/10.1210/endo-118-4-1567

It is a challenging technique.  My tip is to look at the tubidity and pick the right moment when the digestion medium starts to go cloudy.  If you leave it too long, everything is overdigested and youy yield is minimal and what cytotrophs you do get do not do well.  Underdigest and you don't get anything either!  It is highly dependent upon the batch of your digestion enzyme.  Experiment a bit, and once you work out the optimal conditions for your enzyme batch it gets much more reliable.  I also find using placenta collected after elective caesarean section much easier to deal with and more reliable to digest; nor have you got the problem with bacteria, yeast etc with a placenta from vaginal delivery that picks all this up when it passes through the birth canal. Good luck.

Hello

in these articles will be find many protocols about this issues

 Good Luck

http://www.ncbi.nlm.nih.gov/pubmed/19495697

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4497497/

http://www.ncbi.nlm.nih.gov/pubmed/9089768

http://www.nature.com/labinvest/journal/v81/n9/full/3780334a.html

http://link.springer.com/article/10.1186%2Fs12958-015-0070-8