the range of delta-selectivity of linear and cyclic analogues of enkephalin in rat brain was found to be : [ d-pen2 , l-pen5 ] enkephalin ( dplpe ) greater than [ d-pen2 , d-pen5 ] enkephalin ( dpdpe ) greater than [ d-thr2 , leu5 ] enkephalyl-thr6 ( dtlet ) greater than [ d-ser2 , leu5 ] enkephalyl-thr6 ( dslet ) .
C0014298
enkephalin
C0525856
dpdpe