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