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