Hi phaneendra,

presence of a C-terminal ester will accelerate the cyclization of linear peptides,

following reviw article entitled "The Cyclization of Peptides and Depsipeptides" might help you.

http://onlinelibrary.wiley.com/doi/10.1002/psc.491/pdf

And you can check my paper, where i have made cyclic dipeptides from the corresponding linear dipeptides.

http://pubs.rsc.org/en/content/articlelanding/2012/ra/c2ra20342a#!divAbstract

(both the articles are free to access)

Thank You Very Much for the suggestion

If the usual coupling strategy via active esters doesnt work, I would try a ligation between the a.a interested, but it depends on whether you have an N terminal ser, thr, or cys (also His would work but much less).

Thank you Luigi Grassi

Try HOOAt and HOAt