CH2 -- wherein R10 is 2-thienyl, 3-thienyl, 2-furyl, 3-furyl, 2-thiazolyl, 5-tetrazolyl, 1-tetrazolyl; R2 in the above formula is hydrogen or lower alkoxy such as methoxy or ethoxy; R3 is hydrogen, a salt forming group, or a carboxy protecting group. 3.