R23 and {TAIL ~ R26} are each independently hydrogen, formyl, alkanoyl of 2 7 carbon atoms, arylalkanoyl of 8 11 carbon atoms, aryloyl, or {HEAD ~ CO2 R27}  
R23 and { TAIL ~ R26 } are each independently hydrogen , formyl , alkanoyl of 2 7 carbon atoms , arylalkanoyl of 8 11 carbon atoms , aryloyl , or { HEAD ~ CO2 R27 }
OTH OTH 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 OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH