... It can be deduced that the Phe residue at the P,, position 1993 Pharmaceutical Society of ... Chemical shift values are expressed as ppm downfield from tetramethylsilane used as an internal standard (ð ... m), 1.44 (9H, s), 1.32–1.41 (3H, m), 1.79–2.06 (5H, m), 295–3.14 (4H, m), Vol. ...