In other embodiments, {HEAD ~ X2} is selected from {TAIL ~ D leucine}, D valine, glycine and D proline 
In other embodiments , { HEAD ~ X2 } is selected from { TAIL ~ D leucine } , D valine , glycine and D proline
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH