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: ['2497', 'p', 'j', '8229', 't', '3719', '3793', '7937']

j, p, t