On superpotentials for D-branes in Gepner models

A large class of D-branes in Calabi-Yau spaces can be constructed at the Ge pner points using the techniques of boundary conformal field theory. In thi s note we develop methods that allow to compute open string amplitudes for such D-branes. In particular, we present explicit formulas for the products of open string vertex operators of untwisted A-type branes. As an applicat ion we show that the boundary theories of the quintic associated with the s pecial lagrangian submanifolds Im w(i)z(i) = 0 where w(i)(5) = 1 possess no continuous moduli.