It also relates to novel compounds which can be reduced to provide {HEAD ~ a detectable species} at {TAIL ~ a pH} of 9 or less 
It also relates to novel compounds which can be reduced to provide { HEAD ~ a detectable species } at { TAIL ~ a pH } of 9 or less
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH