I . I NTRODUCTI ONHaving a relatively simple chemical structure, chloramphenicol became the first antibiotic to be synthesized by organic-chemical methods (Controulis, Rebstock and Crooks, 1949). A large number of chloramphenicol derivatives was subsequently prepared. Kolosov, Shemiakin, Khokhlov and Gurevich tabulated, in 1961, more than 500 such compounds, and the total number of known chloramphenicol derivatives is, by now, much greater.For many of these substances, data on their growth-inhibitory potencies for bacteria have been reported. Also, after it was recognized that chloramphenicol acts through specific inhibition of bacterial protein biosynthesis (Hahn and Wisseman, 1951; Gale and Folkes, 1953; Wisseman, Smadel, Hahn and Hopps, 1954) and cell-free model systems of protein synthesis were subsequently developed, chloramphenicol derivatives have been tested for inhibitions of such systems. Hence, the chloramphenicol series of compounds appears to be suited to the derivation of structure-activity relationships.The recent identification of a chloramphenicol binding protein which is a constituent of the 50s subunit of 70s ribosomes (Nierhaus and Nierhaus, 1973;Pongs, Bald and Erdmann, 1973) has renewed our interest in these structureactivity relationships and has encouraged us to analyze them with a view to deriving a structural model of a chloramphenicol receptor site which we infer to be located on the peptidyl transferase which is part of the 50s ribosomal subunit.
II. STRUCTURE-ACTIVITY RELATIONSHIPS WHICH DETERMINE INHIBITION OF BACTERIAL GROWTHFirst systematic efforts to derive for chloramphenicol derivatives structureactivity rules for bacterial growth inhibition were made by Hahn (1955), Shemiakin, Kolosov, Levitov, Germanova, Karapetian, Shvetsov and Bamdas (1955, 1956) and Hahn, Hayes, Wisseman, Hopps and Smadel (1956). Both groups of workers arrived independently at the same conclusions; reviews of these conclusions represented the state of the art for several years (Kolosov et al., 1961;Hahn, 1967a). Both groups also called attention to the fact that data-on growth inhibitions by chloramphenicol derivatives had been obtained in many laboratories using varieties of methods and test organisms and could not be considered to be better than semi-quantitative approximations which did not lend themselves to the derivation of quantitative structure-activity relationships.