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