Conformational study of somatostatin analogues in methanol at low temperature

The conformations of three somatostatin analogues were compared in methanol at 193 K. A biologically active cyclic analogue, DC13‐116 ( D ‐Nal 5 ‐Cys 6 ‐Tyr 7 ‐ D ‐Trp 8 ‐Lys 9 ‐Val 10 ‐Cys 11 ‐Thr 12 ‐NH 2 ), and two linear analogues, one biologically active, DC25‐24 ( D ‐Phes 5 ‐Cpa 6 ‐Tyr 7 ‐ D ‐Trp 8 ‐Lys 9 ‐Val 10 ‐Phe 11 ‐Thr 12 ‐NH 2 ), and one with poor biological activity, DC23‐89 ( D ‐Phe 5 ‐Ala 6 ‐Phe 7 ‐ D ‐Trp 8 ‐Lys 9 ‐Thr 10 ‐Ala 11 ‐Thr 12 ‐NH 2 ), were compared. The predominant conformation of the linear active analogue is shown to be the same as that of the active cyclic analogue; they both adopt a β 11 turn/β‐sheet structure. The linear analogue with low activity has a similar conformation, which, however, is less stable.