1. Gregory, H., Hardy, P. M., Jones, D. S., Kenner, G. W., and Sheppard, R. C. (see page 931 of this issue of Nature).
2. Reported at the Seventh European Peptide Symp., Budapest (Sept. 7, 1964).
3. Gregory, R. A., and Tracy, H. J., Gut, 5, 103 (1964).
4. The earlier stages followed conventional routes and are described elsewhere: Anderson, J. C., Barton, M. A., Hardy, P. M., Kenner, G. W., MacLeod, J. K., Preston, J., Sheppard, R. C., and Morley, J. S., Acta Chim. Hung. (in the press).
5. An analogous example of this difficulty is in synthesis of β-MSH; Schwyzer, R., Iselin, B., Kappeler, H., Riniker, B., Rittel, W., and Zuber, H., Helv. Chim. Acta, 46, 1975 (1963).