Cytotoxic principles from the sap of Kalmia latifolia

Examination of the sap of Kalmia latifolia has revealed Grayanotoxin I (1), phloretin (3), and 2',6'-dihydroxy-4-methoxyacetophenone (5) as cytotoxic components. Twenty-one dihydrochalcones have been synthesized and tested for cytotoxic activity. 2'3,3'4,4'-Pentahydroxydihydrochalcone (8) has been found to be cytotoxic and to have marginal activity in vivo. Seven new dihydrochalcones are described.