{HEAD ~ Formation} of an ester or an amide of the disulfide compound led to {TAIL ~ not only prolongation} of the duration but also improvement of absorption characteristics as a result of increase of lipophilicity 
led to
{ HEAD ~ Formation } of an ester or an amide of the disulfide compound led to { TAIL ~ not only prolongation } of the duration but also improvement of absorption characteristics as a result of increase of lipophilicity
HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH