Chemical and biological properties of formyl gramicidins S

The mono- and diformyl gramicidins S have been prepared. Monoformyl gramicidin S retains about 50% of the expected biological activity and the diformyl derivative is inactive. It is therefore, conceivable that both the amino groups equally contribute to the biological activity of the antibiotic. However, monoformyl gramicidin S has been found to form aggregate and this aggregate is more stable under acidic conditions rather than in neutral or alkaline solutions. Denaturing agent urea has been found useful in dissociating the aggregate. The aggregating ability of formyl peptides is at least be due to their formyl groups.