DE 2149070, Witte EC, Stach K, Stork H, Thiel M, Schmidt F, "Phenoxyalkylcarbonsäurederivate und Verfahren zur Herstellung derselben [Phenoxyalkylcarboxylic acid derivatives and processes for the production of the same]", published 1973-04-05, issued 23 April 1978, assigned to Boehringer Mannheim GmbH
US 3781328, Witte EC, Stach K, Stork H, Thiel M, Schmidt F, "Phenoxy-alkyl-carboxylic acid compounds", issued 25 December 1973, assigned to Boehringer Mannheim GmbH