The invention relates to novel erythromycin analogs and azalides, particularly ones with novel C-13 substituents, and to pharmaceutically acceptable salts thereof. The compounds of this invention are antibacterial agents that may be used to treat various bacterial and protozoa infections. The invention also relates to pharmaceutical compositions containing such compounds and to methods of treating bacterial protozoa infections by administering such compounds. The invention also relates to methods of preparing such compounds and to intermediates useful in such preparation.