The present invention encompasses {HEAD ~ structures} of {TAIL ~ the formula} ##STR1## wherein: X is oxygen, methylene, or difluoromethylene 
of
The present invention encompasses { HEAD ~ structures } of { TAIL ~ the formula } # # STR1 # # wherein : X is oxygen , methylene , or difluoromethylene
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH