The active component of acidic actinomycin congener B-1625 FA was obtained by exclusion column chromatography with Diaion HP-20 SS and aluminium oxide TLC, and was considered to be the B-1625 FA
3β already reported. After repeated fractionations by aluminium oxide TLC, its FAB-MS spectrum showed the ion peak at
m/z M+1 1269, C
62H
85O
17N
12 except at
m/z M+1, 1343, C
64H
87O
20N
12. During the purification procedure, FA
3β was found to be converted to another active product in alkaline solution. The conversion product FA-n
1 obtained as a bright orange rhombic crystal was identified with actinomycin X
2 (
m/z M+1, 1269, C
62H
85O
17N
12). Thus FA
3β was presumed to be weakly acidic by the substitution of one proton of actinomycin X
2 by the group of C
2H
2O
3.
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