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