Our main objective is to prepare inhibitors of Protein biosynthesis that will selectively bind to ribosomes from tumor cells without binding to normal ribosomes. We have recently prepared an active carbocyclic puromycin analog which can be used as a model for these studies. By preparing other analogs of this type we can make a wide variety of structural modifications for use in mapping ribosomal binding regions. We plan to find different binding requirements amoung these ribosomes which will enable us to prepare selective inhibitors of protein synthesis in tumor cells.