Dealing with exp functions



Given the following expression F:

(C1) F :  - G1*x6 - 2*a1*DD1*%E^(-2*a1*x4)*(%E^(a1*x4) - 1) - chi*(1-x1)/2;

                        a1 x4        - 2 a1 x4           chi (1 - x1)
(D1)      - 2 a1 DD1 (%E      - 1) %E          - G1 x6 - ------------
                                                              2


I am trying to factor E^(-a1 x4) out of the first term, to get:


                            - a1 x4     - a1 x4             chi (1 - x1)
...)      - 2 a1 DD1 (1 - %E        ) %E          - G1 x6 - ------------
                                                              2

                               - a1 x4 
so as to be able to replace  %E           with one symbol A

Any suggestions to perform such factorization?

thank you 

--
Paolo Pumilia