Antimetabolites produced by microorganisms. XII. (S)-alanyl-3-(.ALPHA.-(S)-chloro-3-(S)-hydroxy-2-oxo-3-azetidinylmethyl)-(S)-alanine, a new .BETA.-lactam containing natural product.:(S)-ALANYL-3-[α-(S)-CHLORO-3-(S)-HYDROXY-2-OXO-3-AZETIDINYLMETHYL]-(S)- ALANINE, A NEW β-LACTAM CONTAINING NATURAL PRODUCT