Molecular Pharmacology, Vol 7, 674-682, Copyright © 1971 by the American Society for Pharmacology and Experimental Therapeutics

Thioxanthones

II. Studies on the Hydrogen-Bonding Capacity of Lucanthone

¹ Hematology Service, Mount Sinai Hospital Services, Elmhurst, New York 11373, and Department of Medicine, The Mount Sinai School of Medicine of The City University of New York, New York, New York 10029

Lucanthone (1-diethylaminoethylamino-4-methylthioxanthone) is a bacteriostatic and carcinostatic agent, and combines readily with DNA. N₁₁-Methyl substitution results in virtual deletion of these activities. It has been postulated that this effect is due to loss of the capacity to form in an intermolecular hydrogen bond.

Suitable investigations of electronic and vibrational spectra indicate the presence of a stable intramolecular amino-carbonyl proton bond in lucanthone. The studies reveal no evidence of interaction between strong hydrogen-bonding acids or bases and the carbonyl or secondary amine substituents.

Consequently, the reduced biological and biochemical activity concomitant with N-methyl substitution is not attributable to a diminished capacity to form intermolecular proton bonds. In fact, the capability of lucanthone in this regard is lower than that of the less active N-methyl derivative, in which the nonbonding 2p orbital of the carbonyl function is free to interact with hydrogen-bonding acids.

Note:
ACKNOWLEDGMENTS I thank Dr. I. B. Weinstein and Dr. E. Hirschberg for supplying lucanthone and its N-methyl derivative, and Mrs. E. Felten for preparing the illustrations.