Burchard Franck (1926-2017).

Abstract

Burchard Frank, Emeritus Professor of Organic Chemistry at the University ofMfnster, passed away on February 21, 2017. He was an internationally recognized natural-product chemist, who made important contributions to the field of biomimetic transformations of alkaloids, as well as the areas of pigments and toxins, and porphyrinoids. Burchard Franck was born on May 6, 1926 in Hamburg. Already in his childhood he came into contact with chemistry, since his father, who earned a PhD in chemistry from the University of Kiel, was a chemistry teacher and later the head of a high school. However, before he could start with his own studies he had to serve in the army at a very young age, and after the end of World War 2, he was a prisoner of war. Finally he commenced his studies in chemistry at the University of Hamburg, which was almost completely destroyed at that time, making his training rather difficult. After completing his diploma with Rudolf Tschesche, he moved to Göttingen, where he received his PhD for work on the red antibiotic rhodomycines carried out under the guidance of Hans Brockmann. The University of Göttingen was one of the few universities that had not been destroyed in the war, and Franck always praised his stay at this school as the most wonderful experience in his life. In 1959 he completed his habilitation with independent work on the biosynthesis of piperidine alkaloids from Sedum acre. Only a few years later, he moved to the University of Kiel. In 1968 he accepted a call to the University of Münster as the successor of Fritz Micheel and Director of the Institute of Organic chemistry, where he remained until his retirement. In between he received offers to move to the Universities of Bonn and Göttingen. A very important tool for Franck's work in the field of biosynthesis was a radionuclide laboratory, and he was able to convince the authorities to provide these rather expensive facilities. A second essential technique was mass spectrometry, for which he always had the newest generation of instruments. Franck's entire scientific career was focused on natural-product chemistry. After his work on piperidine alkaloids, he moved to the tetrahydroisoquinoline alkaloids, where he impressed the community by his outstanding work on biomimetic transformations. He was able to show that alkaloids from the aporphine and morphine type can be obtained from benzyltetrahydroisoquinolines by phenol oxidation after protecting the tertiary nitrogen atom as a quaternary salt. This work, which he presented in a lecture in Freiburg (where I was studying), impressed me so much that I moved to Kiel to become one of his students. Besides alkaloids, another important group of natural products that caught his interest early on were the pigments and toxins of fungi. In 1960, he started working on the ergochromes isolated from Claviceps purpurea and invented a nomenclature for the highly complex dimeric tetrahydroxanthenons (ergochroms, secalonic acids), which is still in use. The compounds were synthesized for the first time only recently. Franck showed that anthraquinones such as emodine are key intermediates in their biosynthesis. Several mycotoxines were also been isolated from fungi and synthesized; in addition their biosynthesis was investigated. In the latter part of his career, Franck moved to the area of porphyrins, where he again performed exciting work. For the investigation of the biosynthesis of these natural products, he carried out an elaborate synthesis to prepare a specifically 14C-labeled [α,γ-14C2]uroporphyrinogen III, and with feeding experiments, he could show that this compound is incorporated into heme without isomerization. Moreover, among other examples, he prepared a hexavinologous porphyrin with an aromatic 30 π system as well as N,N′-bridged porphyrins in a biomimetic fashion. In addition, he synthesized coproporphyrins for photodynamic cancer therapy. Besides his scientific work, Franck was a great teacher and was able to explain chemistry in a very clear and profound way. His lectures were always so perfectly presented that the notes could be used as a textbook. For this reason, he was invited as visiting professor by many universities in the USA, China, and Switzerland. He was a referee for the Deutsche Forschungsgemeinschaft for many years, and he received several awards, including the Richard Kuhn Medal of the Gesellschaft Deutscher Chemiker (GDCh; German Chemical Society) and the Windaus Medal of the University of Göttingen. Burchard Franck, who grew up in the city of Hamburg, was a typical north German with a somewhat reserved character, but he was accepted and greatly respected by his colleagues. He devoted his life to research and teaching and was always supported by his wife Dr. Renate Franck.