You have made one of the most common mistakes. In ABAP almost at all the places be careful with SPACE. You need to have a space in method calls so just have a space before and after the brackets as below −
SELECT SINGLE * FROM EKPO WHERE EBELN = GT_MSEG-EBELN AND EBELP = GT_MSEG-EBELP AND NOT ( F1 = 'value' AND F2 = '0' )