The present invention relates to novel arginine analogs, and methods for their synthesis and use. Such analogs are designed to provide a protected or free thiol (--SH) group, thereby providing a convenient linkage chemistry for coupling to a suitable group on a target such as a protein, polypeptide, detectable label or solid phase, and at a site distal to the guanidino group. Arginine analog conjugates are useful for generating antibodies that can bind specifically with dimethylarginine, which can be detected using such antibodies in immunoassays.