Differentiate the number e (exp(1)) symbolically

Question

I want to take the derivative the a function that includes the number e (exp(1)). How can I solve symbolically using e (i.e., not decimal numbers). For example:

syms x
e=exp(1)
diff(e^-x)

Answer 1

What if you do

 syms x;
 e=exp(sym(1));

Answer 2

It's rarely a good idea to assign predefined constants to variables when using the symbolic toolbox:

diff(exp(-x))