Siamycins I and II, New Anti-HIV-1 Peptides: II. Sequence Analysis and Structure Determination of Siamycin I.

Wehave previously reported on the preparation and initial characterization of the structure and biological activity of siamycins I and II1}.Here, we report on the novel strategy used to rapidly determine the primary, secondary and preliminary solution structure of siamycin I using a multidisciplinary approach that utilized primarily MSand NMRdata.The presence of three internal covalent cross-linkages found in siamycin I made structure analysis by traditional methods difficult, particularly in the TV-terminal region.Lowresolution full scan and product ion mass spectra were acquired on a Sciex API /// tandem quadrupole mass spectrometer equipped with an Ionspray (pneumatically assisted electrospray) interface.Samples were analyzed in the flow injection mode using a 0.1%