followed by filtration of the desired salt and vacuum drying.,' Then, 4.5 g (61 "01) of 2-butanol and 2.3 g (20 "01) of the formamidinium salt were stirred under reflux for 21 h. The mixture was cooled to room temperature, washed with 15 mL of Et,O, and concentrated under vacuum. The residue was dissolved in 2 mL of MeOH and chromatographed over silica gel with 1 3 1 CH2Cl2/MeOH eluent. Weobtained 1.29 g (8.4 mmol, 42%) of isouronium salt 8 as a highly hygroscopic, glassy solid (under vacuum), that fused to a slightly yellow oil in the atmosphere. J = 6 Hz, CHCH,); 1.45-1.65 (m, 2 H, CH,); 4.75-4.95 (m, 1 H, CH); 8.67 (br s, 4 H, 2N+H2). to (S)-8 were carried out analogously. Detailed descriptions of the optical rotations of these materials appear in the text.3-(2-Butoxy)-3-chlorodi.ziriw (9). The Graham oxidationI8 was carried out on 1.29 g (8.4 mmol) of isouronium salt 8. The salt was dissolved in 5 mL of DMSO, then, 15 mL of pentane and 0.1 g (2.4 "01)of LiCl were added. The mixture was stirred and cooled to 5 ' C while 220 mL of 12.5% aqueous NaOCl was added dropwise. The reaction temperature was kept at 10-13 ' C during the addition. Stirring was continued for 20 min at 13 OC after addition of the hypochlorite. Then, 150 mL of ice water was added, the pentane layer was separated, the aqueous layer was extracted with 10 mL of pentane, and the organic extracts were combined. The resulting pentane solution of 9 was washed with 50 mL of brine and then dried over CaCI,. Higher boiling solvents (MeCN, I-butanol) could then be added and pentane removed at 0 ' C under aspirator vacuum, to afford solutions of diazirine 9 in other solvents. The UV and NMR spectra of 9 are described above; it was too unstable to chromatograph. (a-9 was prepared from (S)-8 in the same way.(neat)), 6.2 mL (5.0 g, 67.5 mmol), and 4.6 mL of dichlorophenyl-'H NMR (DMSO-d6): 0.84 (t, J = 7 Hz, 3 H, CHzCHJ; 1.21 (d, (~)-2-chlorobut.ne (12). (R)-(-)-2-Butanol (AIdrich, [aI2'D -12.8' Abstract: We have developed an integrated approach for investigating the 'bioactive conformations" of the main chain and side chains for the somatostatin analog ~[Pro~-Phe~-~-Trp~-Lys~-Thr~~-Phe'~]. A series of analogs have been synthesizedincorporating a-methylated and 8-methylated residues at positions 7,8, and 11. These analogs display dramatic differences in in vitro binding affinities for somatostatin receptors. Using 500-MHz 'H NMR and computer simulations, we have assessed the effect of main chain and side chain chiral methylations on the overall structure. The analyses of the changes of side chain topologies and subsequent binding affinities in the 8-methylated analogs have provided definitive evidence about the 'bioactive conformation" of the side chains of Phe7, Trp8, and Phe". The analyses of the a-methylated analogs have defined a 'folded" feature for the peptide backbone. From this study, we have proposed a binding 'pocket" for somatostatin analogs which consists of the side chains of Trp' and Lys9, the peptide backbone, and the side chain of Phe" in a...