Purification Methods
Purify gramicidin A by countercurrent distribution from *C6H6/CHCl3, MeOH/H2O (15:15:23:7) with 5000 tubes. Fractions are examined by UV (280nm) of small aliquots. Separation from gramicidin C and other material occurred after 999 transfers. [Gross & Witkop Biochemistry 4 2495 1965, Bauer et al. Biochemistry 11 3266 1972.] Purify it finally by recrystallisation from EtOH/H2O and dry it at 100o/10-2mm over KOH. It forms platelets m 229-230o. It is almost insoluble in H2O (0.6%) but soluble in lower alcohols, dry Me2CO, dioxane, acetic acid and pyridine. The commercial material is more difficult to crystallise than the synthetic compound. [Sarges & Witkop J Am Chem Soc 86 1861 1964, 87 2011, 2020 1965.] It has characteristic [] D20 +27.3o (c 1.3, MeOH) and UV max at 282nm ( 22,100). The N-carbamoyldeformyl gramicidine A precipitates from EtOAc/pet ether (b 40-60o). [Beilstein 26 III/IV 4273.]
