Definition: In this task, you are given an input list A comprising of numbers and alphabets. You need to extract and sort the unique alphabets in the list. The alphabets in the input list will only be in lowercase. Return -1 if there is no alphabet in the input list.
Input: ['4749', '4607', '625', '6907', 't', 'b', '8479', '6505', 'r']

b, r, t