The present invention provides novel thioester derivatives of thiazolyl acetic acid of the general formula (I),wherein, R1 represents H, trityl, CH3, or CRaRbCOOR3, in which Ra and Rb, independently of one another, represents hydrogen or methyl and R3 represents H or C1-C7 alkyl; and R2 represents C1-C4 alkyl or phenyl. The invention also provides a method for preparation of the thioester derivatives and reaction of the thioester derivatives with cephem carboxylic acids to produce cephalosporin antibiotic compounds having general formula (II),wherein, R1 represents H, trityl, CH3, or CRaRbCOOR3, in which Ra and Rb, independently of one another, represents hydrogen or methyl and R3 represents H or C1-C7 alkyl; R4 is CH3, -CH=CH2, CH2OCH3, CH2OCOCH3,and R5 is H or a salt or a carboxylic protecting group, comprising,acylating a compound of formula (III),wherein, R4 and R5 are defined as above, and R6 is H or trimethylsilyl;with a compound of formula (I).