{HEAD ~ The compounds} have {TAIL ~ the formula}: ##STR1## wherein: the dashed line indicates either the 4,5 unsaturated or the 4,5 dihydrofuranone ring 
have
{ HEAD ~ The compounds } have { TAIL ~ the formula } : # # STR1 # # wherein : the dashed line indicates either the 4,5 unsaturated or the 4,5 dihydrofuranone ring
HEAD 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 OTH OTH OTH OTH OTH OTH