  I review some marginal deformations of SU(2) and SL(2,R) Wess-Zumino-Witten
models, which are relevant for the investigation of the moduli space of NS5/F1
brane configurations. Particular emphasis is given to the asymmetric
deformations, triggered by electric or magnetic fluxes. These exhibit critical
values, where the target spaces become exact geometric cosets such as S2 =
SU(2)/U(1) or AdS2 = SL(2,R)/U(1)-space. I comment about further
generalizations towards the appearance of flag spaces as exact string
solutions.
