SEARCH FOR THE PHARMACOPHORE OF THE K+ CHANNEL BLOCKER, APAMIN

The suggestion that the arginine residues, 13Arg and 14Arg, in the octadecapeptide apamin 1 are critically important to its action in blocking Ca2+-dependent K+ channels (and hence part of the 'pharmacophore') has been investigated by examining small peptides containing Arg-Arg or Lys-Arg. Bisguanidine derivatives modelled on the Arg-Arg partial pharmacophore have also been synthesised and tested; in particular, N-(2-guanidinoethyl)-3[N1-(2-guanidinoethyl)carbamoyl]-trans-propenamide 11 and its higher homologue 12. None of the compounds showed more than weak activity (K(i) > 10(-5) M) indicating that although the Arg-Arg fragment may be necessary, it is not a sufficient atom grouping for the pharmacophore.