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