These new drugs are {HEAD ~ markedly improved analogs} of {TAIL ~ previously known fluorenone compounds} that were never commercialized or developed into medically useful treatments 
of
These new drugs are { HEAD ~ markedly improved analogs } of { TAIL ~ previously known fluorenone compounds } that were never commercialized or developed into medically useful treatments
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH