Vladimir Prelog (1983) - A Look Back at 118 Semesters of Studying Chemistry (German Presentation)

Mr Chairman, Ladies and Gentleman, when I was invited this year to hold a lecture in Lindau my first thought – with all the young scientists present here today – was to talk about the huge changes that have taken place in the views held, the methodology and in the purpose of organic chemistry over the last 50 years. However, I came to the conclusion that this was too great a task and restricted myself to describing only a few of these changes, with examples from my own scientific career. And even this task can only be dealt with superficially in the short time available. The selection of examples is by its nature very subjective. We have a saying that the young always overestimate their future and the old their past. May I ask you right at the start of my talk to indulge me if I unavoidably slip up here a little. My first slide quotes from an old book on alchemy - I think it needs to be a little darker. I use this to show that even back then the study of chemistry was changing rapidly. Conducting research in the field of chemistry means you remain an eternal student. To justify my title I need to briefly outline my career which will form a time line for my elaborations. I was born in Sarajevo in 1906, then the capital city of Bosnia and Herzegovina which was a province of the Austro-Hungarian Empire in those days. The city had a bad reputation in the Western world, something I became very much aware of when, after my first visit to the United States of America in 1950, I had to obtain a so-called sailing permit, meaning confirmation that I had paid my taxes in the States. The conversation with the somewhat elderly tax official in charge went something like this: Tax official, "Where are you from Professor?" Me, "Zurich. He said, "Zurich, Sweden?" Me, "No, Zurich Switzerland." He was evidently somewhat put out,"But you were not born in Zurich. Where were you born?" Me: "Sarajevo". Tax official, with relief: "Ha, that's the place where all this mess started." He was obviously referring to the murder of the heir to the throne and his wife, considered then and now as the direct cause of World War I. Here it is worth mentioning that, as a school pupil, I stood not far off from where the assassination took place with the task of throwing flowers in front of the illustrious visitors' carriage. Here, as so often in later life, I was a bystander and onlooker of momentous events. Although it determined my choice of degree studies, I need to leave out the period between 1914 up until the autumn of 1924 which took 118 semesters at the technical University of applied sciences in Prague. I would briefly like to emphasise the important role which secondary school teachers exercised on their pupils' choice of career. I had an outstanding chemistry teacher called Ivan Kuria. Under his tutelage, I wrote my first completely trivial tract on chemistry at the age of 15. The fact that a prestigious chemistry journal accepted this work underscores the then very low standard of writing on chemistry. During the first 3 semesters I devoted my time to very big problems of natural science and philosophy. My hope was that I would one day succeed in contributing to solving these problems. My favourite books were Poincaré's "Science and Hypothesis" and Mach's "Science of Mechanics. A Critical and Historical Account" and the like. There was a gaping void between the spiritual heights of my nightly reading sessions and the day-to-day grind in the anorganic and analytical laboratory. Kant aptly expressed my feelings back then, "Concepts without percepts are empty; percepts without concepts are blind." In the fourth semester, when I took the post of assistant of the laboratory for organic chemistry where I was doing my internship, I was lucky enough to find a mentor in Rudolf Lukeš who rescued me from this unhappy situation of blindness and vacuity. I would like to show you a picture of Mr Lukeš. He was to become not only my teacher and but also my friend up until his premature death in 1960. I think that if you're talking about someone it is always interesting to see a photo, his face, as I find the human face a source of great fascination. Before I met Lukeš chemistry seemed to be a smorgasbord of endless bondings and reactions which one had to learn by heart in order to function in this field. Lukeš introduced me to the wonderful classification of organic chemistry which permitted order to be imposed on what was already known as well as allowing us to step beyond the confines into the unknown. He also introduced me to the art of organic-chemical experimenting by teaching me how to blow glass as an amateur, how to drill a cork lege artis, perform gentle distillation and so much more. In the evenings when work had officially ended I assisted him in his research and, while still a student, published several articles together with him. I remain convinced today that being an apprentice to a master whose competence and authority one accepts is the most wonderful way to learn how to research – just like the artists and sculptors of the Renaissance who were initiated into the secrets of their art by their predecessors. My doctoral supervisor was not Lukeš but, as was customary, the professor of organic chemistry who was Emil Votocek. He had been a student of Bernhard Tollens, a Gerrman chemist famous for developing sugars. After the groundbreaking work of Emil Fischer on sugar and other carbohydrates, the work of Lukeš and Votocek seemed epigonic to me. I therefore asked him to assign me another topic from a different field for my thesis. I swiftly solved my task which was to analyse the constitution of an algycon and passed my PhD exam within the shortest period of time possible under exam regulations at the end of the 10th semester with summa cum laude. The year 1929, which was when I did my PhD exam, marked the year of the Great Depression. Consequently, I was unable to find a job at a university or any other institution that would allow me to dedicate myself to researching organic chemistry. I counted myself lucky when a school friend of Lukeš entrusted me with developing 2 rare compounds which were commercially unavailable for his two chemical businesses in a small laboratory to be set up in Prague. After work I had modest opportunities in this laboratory of doing research, and my employer was my first doctoral candidate, which was a delicate task. At that time I had to decide which problem was important enough for me to while away the night working on it. My interest in alkaloids, inherited from Lukeš, combined with the aspiration of doing something important for mankind were what motivated me to work on quinine and the alkaloids of China bark. Back then quinine was still the most important anti-malarial treatment; its composition was known but not its spatial arrangement, its configuration. Synthesis as a method was predefined by the work of Paul Raabe but the basic material for it was difficult to access. Could I have the next slide please. Next slide please. I worked on quinine and the problems associated with it slowly over a period of 7 years in Prague. I continued my work for 5 years in Zagreb in Yugoslavia. Here I had been offered the position of university lecturer in response to the work I had done and my publications. I accepted the job with huge enthusiasm. What I did not know was that the job entailed the duties of a regular professor, i.e. lectures, examinations and tutoring, remunerated with the salary of a poorly paid assistant. However, the job offered one huge advantage: I was free to research anything I pleased. I could do anything that my ridiculously small budget permitted but without having to ask anyone or report back. With the aid of a few young enthusiastic colleagues, we made good headway with our basic research at the university. I would like to illustrate the work I did in Prague and Zagreb with a few formulae, just enough to show how they potentially increase in complexity. At the top we have the formula for quinine. We discovered that the syntheses conducted to date in this series can be solved very easily with the constitution of the quinolin proportion on your left. However, since quinuclidine syntheses from easily accessible material was not possible, and because quinine had to be produced very cheaply as a remedy for malaria, we applied ourselves to producing these compounds. These are so-called bicyclical bases with nitrogen on the branched atom. We learnt a great deal in the process of producing the compound dichlordiethylamine, N-methyl-dichlordiethylamine which you see on the right. We discovered that it is extremely toxic. Our hands were always covered in blisters when working with this compound. It was later used as a cure for certain types of cancer, and many similar compounds have been manufactured for this purpose. In those days, we had no idea what kind of a compound this was. One problem, which was independent from the chemistry of quinine and which we successfully solved in Zagreb, was the first synthesis of adamantane, an unusually symmetrical hydrocarbon which had been isolated by Stanislav Landa from crude oil a few years before while I was still there. The next slide shows the stereo formula of adamantane and the lovely tetrahedral crystals from which the formula for adamantane was intuitively derived. Adamantane has become a popular object of research in organic chemistry after Paul Schleyer invented a beautifully simple method for manufacturing it. The good progress we made with our work was overshadowed by the dark clouds which spread first across Europe and then later enveloped the whole world. The outbreak of war broke in 1939 and the occupation of Yugoslavia by German troops in 1941 put a stop to research work in Zagreb. The pharmaceutical company which supported us was nationalised and showed no interest in further collaboration. An invitation from Richard Kuhn, president of the German Chemical Society, to lecture in Germany and one from Leopold Ružicka to visit him in Switzerland allowed me to enter Switzerland by legal means. Like many fellow scientists, I found sanctuary in ETH's laboratory for organic chemistry and the opportunity of continuing my research. The convergence of various favourable circumstances made this easier. Ružicka already knew me personally as I had been a guest in his laboratory for several months in 1937. Shortly before I arrived in Zurich in 1941, a larger group of colleagues had left the laboratory to go to America. They no longer felt safe in Switzerland. Some of them played an important role in building up the pharmaceutical industry on the other side of the Atlantic. George Rosenkranz and Stefan Kaufmann developed Syntex in Mexico into a global company. Max Furter and Wolf Moses Goldberg organised research at Hoffmann-La Roche in the United States, and Leo Sternbach later discovered Librium and Valium there, an immensely important discovery. This exodus left a vacuum in ETH's laboratory for organic chemistry which made it easy for me to find work there. I took up my tasks as a teacher at ETH, went on to do my doctorate, became honorary professor, associate professor and then, finally in my 52nd semester, full professor. In 1957 I took over laboratory for organic chemistry as successor to Ružicka, which brought my incompetence to new levels. My efforts to make good by introducing collegial laboratory management from which I would be excluded were crowned with success in 1964. I retired in 1976 and, as our school does not recognise the status of an emeritus professor, I am a guest student again at the end of my 118th semester. This semester my sole obligation is to hold a seminar on 1 July. The 32 semesters which I spent in Prague and Zagreb could be described as the Middle Ages of organic chemistry. The impressive central nave of the cathedral of structural organic chemistry had been almost completed built on the strong foundations of old masters. Back then the task was to build the lateral knaves and do the interior work. The building materials used were largely made up of natural substances as well as increasingly of the numerous compounds which developed swiftly, enabled by synthesis. However, the time was approaching for the cathedral to be rededicated to its original purpose: to recognise and learn to understand the material foundations of life in all its aspects, from reproduction through to consciousness. This is – and will always be – a valid justification for dedicating one's whole life to the study of chemistry. Nobel laureate Sir Cyril Hinshelwood expressed this beautifully in his presidential lecture for the Chemical Society: Its followers seek to know the hidden causes which underlie the transformations of our changing world, to learn the essence of the rose's colour, the lilac's fragrance, and the oak's tenacity, and to understand the secret paths by which the sunlight and the air create these wonders." He also wrote these words: But it is revealed only to those who seek it for itself." When I arrived in Zurich in 1941 Ružicka, as we will see on the next slide, was at the peak of his scientific career two years after winning the Nobel prize. ETH's laboratory for organic chemistry which he headed enjoyed a remarkable tradition. It was an indescribable joy for me to be permitted to work in this laboratory which, for conditions back then, was luxuriously equipped. I just want to briefly explain: I think the slide of Mr Willstätter has already disappeared. He won the Nobel prize for his work on plant pigments, particularly chlorophyll. This is Hermann Staudinger, Ružicka's teacher, who was awarded the Nobel prize for his contributions to macromolecular chemistry which were fundamental. The last one is Richard Kuhn - next slide please - who received the Nobel prize mainly for his work on vitamins. As far as my work schedule was concerned, I agreed with Ružicka that I would fill a few of the gaps myself and continue the experiments on organ extracts which others had begun. I also wanted to work on alkaloids together with a few other young colleagues. With the support of the Rockefeller Foundation, Ružicka had had larger volumes of organ extracts produced in the United States. His hope was use modern separation processes, such as molecular distillation and chromatography, to find the unknown hormones that he presumed these extracts contained. Even before I arrived in Zurich the experiments were not going smoothly, which meant no one envied me the job when I got it. My first task was to screen extracts from several tons of pig testicles for novel active ingredients which, despite my diligence, was not successful. We had a minor success in isolating a substance which had strongly musky odour which turned out to be a steroid derivative related to the first male hormone androsterone isolated by Adolf Butenandt from urine. As you can see from the slide, there is a formal similarity between this compound seen down here and the more strongly smelling ketone more to the right, and the natural musk civetone discovered by Ružicka. After many years had elapsed, when I had almost forgotten that I had isolated 3-alpha androstenol all by myself, I found out that it was being used successfully as a sexual attractant in the rearing of pigs. Just as amusing was the information that it is also present in truffles, which is the reason why pigs are able to root out truffles under a thick layer of earth. The ostentatious claim recently featuring in advertisements that it also makes men irresistible is not something I think credible. At least, this is not what I have experienced. (Laughter) In any case, it is interesting that there are many people, such as Ružicka himself, who cannot smell 3-alpha androstenol, which is apparently due to a genetically determined anosmia, as we later found out. To give you the opportunity of testing this anosmia yourself and the smell itself we are going to distribute impregnated strips of filter paper. I have dedicated so much time to this one substance with the aim of illustrating the theory that one can never know what can come of even the smallest of discoveries. Please take a good sniff at this paper strip. You will find that, whereas some of you will not be able to smell anything at all, others of you will detect a quite strong odour, which I would like to have your opinion on. I have consoled myself when faced with the very modest results from working on organ extracts by the progress made in alkaloid experiments. Here it was a question of discovering the constitution and spatial arrangement of several well-known, easily accessible alkaloids, of China bark, for instance, of Strychnos alkaloid, solanidine from potato sprouted seeds, Veratrum alkaloid and Erythrina alkaloids, among others. Just leave the slide for a moment please. Let's look more closely at these alkaloids, at the way they become increasingly complex. Solanidine, for example, is still very similar to the compounds which we first showed. Here you see a picture of my role model and fictitious teacher in the field of alkaloids. We were brought closer together through our work on Strychnos alkaloids and developed a personal relationship akin to an emotional roller coaster. The work on the China, Strychnos and Veratrum alkaloids which you have seen brought me under the influence of two young teachers who strongly promoted me in my studies of chemistry. The first you will see is Robert Burns Woodward, and the second I would like to introduce here is Sir Derek Barton, both of whom published work jointly together with us. During the 1950s, the research scene in the field of organic chemistry underwent a dramatic change. Using chemistry to determine the constitution, which formerly played a huge role, was replaced – first slowly and then ever more swiftly – by physical methods. It became possible to determine the structure of molecules more swiftly and clearly, particularly with the aid of diffraction methods and especially by using x-ray analysis, than by using purely chemical means. My colleague Professor Jack Dunitz chose the following analogy to illustrate this: who has been locked in a pitch dark room and given the task of exploring this room. If allowed to wander around long enough he will most likely knock over various objects such as vases and standard lamps. Ultimately, however, he will be able to describe the room very accurately. The x-ray scientist in the same room for the same purpose simply switches on the light." X-ray scientists were then joined by molecular spectroscopists who search the room by torchlight and are often in a position to reconstruct a quite accurate overall picture from the partial knowledge gained from this process. The introduction of molecular spectroscopy and x-ray analysis signified a change for the chemist equivalent to the introduction of firearms in the art of war. Victories, formerly the province of heroes with the exceptional physical strength and courage, could be then be won by average soldiers with good weapons. This development resulted in a number of gifted chemists turning their backs on natural product chemistry because they felt it lacked the intellectual satisfaction which they found in constitutional chemistry. I recall that Saul Winstein, another of my teachers who has since died, once asked me a question in 1951 – next slide please: Because my preference for natural substances is emotional rather than rational, I had to think about it first. I came to the realisation that natural substances are the result of evolution lasting 10^17 seconds or 3 billion. They harbour great wisdom, even if we mostly fail to understand them. If we want to learn about the material foundations of life it makes sense to study natural substances. We therefore remained true to natural product chemistry. Although constitution discovery formerly held in such high regard lost status as an intellectual game, the tasks that remained were just as important and interesting: the isolation of new natural substances and new breeds of substances, the swiftest possible discovery of their structure using the most economical and reliable methods, researching their biogenesis and ultimately – and perhaps most importantly – the clarification of their role in the biological activity and their mechanisms. This signifies enough important and interesting work for generations of researchers, who can only appreciate the fact that the determination of constitution which used to take up so much of their working life has been made so much easier. In fact, it has made it possible to solve the other tasks. An ethical and social aspect of this development deserves a special mention. Whereas the equipment needed for organic chemistry before the war was simple and cheap, the new physical methods required increasingly more expensive instrumentation as well as the specialists who know how to operate them and interpret the results accurately. This has sent research costs spiralling, by a factor of between 10 and 100. Consequently, and quite logically, funding parties, public institutions and the various funds who are all not versed in the art of science have begun to ask whether the huge amounts spent are also used for the intended purpose. For this reason, ever more detailed projects for research planned and increasingly detailed reports on research conducted are required. These reports are then often assessed by experts and non-expert people who lack relevant competence. Alongside this desire for greater transparency, there was a demand for all research to be done in the interest of society, to which firstly insecure politicians acquiesced and secondly the public authorities in many countries. As a result, many scientists conducting basic research mourn the partial loss of freedom and take a decided stand against the demand that their work needs to be relevant to society. The renowned physical chemist and philosopher Michael Polanyi had the following to say on this topic: this generation will find, too late, that it has opened wide the pass to the barbarians." Allow me to briefly describe how we have adjusted to the new situation. The first step was to change the source of the natural substances that we investigate. Ružicka and his team worked exclusively with natural substances from the world of plants and animals. Prompted particularly by the discovery of antibiotics such as penicillin and others, we have begun to work more systematically on cultures from microorganisms and microbial metabolites. These cultures soon turned out to be treasure troves of new and unusual natural substances. We have stopped all the work on plant and animal natural substances such as alkaloids, terpenes and steroids, in order to dedicate ourselves exclusively to microbial metabolites. In view of this, we needed active support from microbiologists, which we found in the person of Professor Ernst Gäumann and his students at ETH. We were given further important material and technical assistance by the pharmaceutical industry which, understandably, showed great interest in this research. During the harmonious collaboration between the microbiologists, organic chemist and the pharmaceutical division of Ciba respectively Ciba-Geigy which was ongoing until my withdrawal, we defined the structure of numerous, partly completely new microbial metabolic products and investigated their reactions. I would like to make special mention of 2 groups of these compounds which have risen to prominence. Over the course of our work, the microbiologists came across a new, particularly potent ferrous antibiotic. Attempts to purify it delivered conflicting results: the antibiotic disappeared during certain purification operations only to reappear in later purification phases. Hans Zähner subsequently found the solution to the puzzle. The antibiotic was accompanied by an antagonist, a ferrous growth promoter. Depending on the proportion of the growth promoter to antibiotic in the compounds we looked at, we found either an antibiotic efficacy or an inactive preparation. The actual proportions were even more complicated because the sensitive antibiotic was transformed into the growth promoter during certain purifying operations. Having ascertained these facts, the antibiotic, the ferrimycin and a huge cluster of associated growth promoters, which we call ferrioxamine, were isolated in a pure form and their structures determined. The next slide shows the structures of several ferrioxamines, with ferrioxamine B as the main product, and the slide after displays the structure of ferrimycin. At the top you can see that the growth promoter is also contained in ferrimycin. The ferrioxamine was used to produce non-ferrous desferrioxamine B which forms remarkably stable complexes with iron(III) ions which are soluble in water as opposed to other biologically important ions such as calcium(II), zinc(II) and so on with which it forms only weak bonds. Next slide please. Here you see a series of figures - it is incredible: iron has a stability constant of over 10^30, so it can be complexed with anything made of iron in a city. This property was used by the haematologists Heilmeyer and Wagner in Freiburg, Breisgau, to remove pathological iron from the human body which had collected in the liver, pancreas and other organs, as well as in the eyes, with certain lethally contracted diseases. We, or rather the haematologists, have therefore found a remedy which can save many people otherwise fated to die. A second group of microbial metabolites whose structures we determined and whose reactions we studied are the rifampicins. These compounds were isolated from the cultures of Nocardia strain, isolated by the chemists of the Italian pharmaceutical firm Lepetit. When I was asked to elucidate the structure of rifampicins, Wolfgang Oppolzer, now professor in Geneva, assisted us in solving this problem within a relatively short space of time in a hard race against x-ray data analysers. Based on the structures shown on the slide, the chemists of Lepetit and Ciba-Geigy then produced several thousand rifampicin derivatives and tested them in order to improve their therapeutic properties. One of these derivatives, namely rifampicin, is used today as a first-line medication in the fight against tuberculosis and leprosy. Beyond this, rifampicins and their derivatives are also interesting to molecular biologists because they act as inhibitors of the reproduction of certain nucleic acids. Indeed, these compounds, not only rifampicin but also a number of others such as Isoniazid, have somewhat changed the world. Violetta in La Traviata could be treated and healed as an outpatient today. Whether she would have been happy with her Alfredo is another question. (Laughter. Applause) I believe that these examples are a good illustration of how basic research in the field of organic chemistry can be relevant for society even though this was not their original purpose. All we wanted to do was to determine the structures. Apart from this, they help us to understand the material foundations of life and therefore of our existence. This is an important part of our culture on a par with art and the humanities, which is something that most people who are not chemists cannot or are unwilling to understand. Indeed, chemistry can be viewed as fundamental to a strain of science which does not exist yet called molecular theology. In my talk today I have so far intentionally avoided the word stereochemistry though we have been extremely active in this field since the end of the war. It is not possible to work with natural products chemistry on a broad basis without dealing with the topic of stereochemistry. Having studied the pertinent literature I soon found that there are still many basic tasks waiting to be solved in this field. As the prize for experiments of stereochemistry on organic compounds and reactions has already been pledged, let us list some of the problems which we are working on more intensively in order to demonstrate their diversity. Firstly, the non-classical arrangement of the 8- to 12-membered rings and their influence on physical properties and reactivity, illustrated on the next slide through the dependence of the stability of cyclical cyanhydrin on the size of the ring. There is therefore a tension not formerly identified which we call non-classical tension. Mr. Braun who is here today and who detests everything non-classical has given an easily memorable name to these tensions: FBI tension. The non-classical tension associated with transannular substitution and elimination reactions is shown on the slide through 1.5 and 1.6 hydrid shifts in cyclodecyne carbocation. And thirdly: The regularity of the spherical sequence of asymmetrical synthesis is based on the relative space taken up by the ligands of the asymmetry-inducing asymmetrical atom which permits the prediction of enantioselectivity. As an example, this the slide shows a rule, graciously labelled by my kind colleagues as Prelog's rule, and on the next which is attached to the asymmetrical carbon atom bigger and bigger. In the first form you have a phenyl, then a trimethylphenyl and finally a tricyclohexylmethyl, and an enantiomeric excess can be enlarged from 3 to 66 in this way. Fourthly: The regularity of the steric sequence of microbial and enzymatic reactions, particularly the reduction of carbonyl compounds through oxidoreductases. On the slide here we have the stereoselectivity of 2 enzymes, specified by the characteristic diamond lattice section which we introduced. Each enzyme has its own characteristic diamond lattice which is rather like a finger print of its reactivity. All this work was aimed at reducing the frightening scale of diversity in the feasible spatial arrangement of atoms in the molecule to a treatable dimension which allowed the behaviour of the molecules to be derived. In the process, the Scylla of uselessness and the Charybdis of inaccuracy needed to be avoided, as if it is too complex it is generally not much use, and if it is too simple it is often wrong. The system for specifying the configuration of stereoisomers developed together with Robert Sydney Cahn and Sir Christopher Ingold – on the next slide the ascetic face of Sir Christopher and the one after shows Cahn correcting our manuscript in my hotel room in Sydney. That's Cahn in the front and behind is his mirror image and right at the back is the mirror image of the photographer. During the process of building the system we needed to understand the fundamentals of stereochemistry and examine its scope and boundaries. We became aware that, in specifying the stereoisomers, we were also specifying the chirality of the molecules or their parts. This allowed us to popularise the term "chirality" first coined by Lord Kelvin last century – next slide please – which he defined as follows among the chemist community. I would like to focus on the term chirality and its typology by using three works of art on the last slides. The Swiss painter Hans Erni depicted the paraphernalia which, in my view, is needed for its specification. The mirror image – please leave it for a moment. Could I have the slide before again please. You see here 2 irregular mirror image tetrahedrons, 2 hands and human intelligence symbolised by the girl's head. On the next slides you will see works of art which were created over a huge time span of 3000 years which show that you can easily get into difficulty with chirality. The first slide is a relief image of Egyptian King Sethos I, with the right hand on the left side and vice versa. Next we have a painting by Chagall, Chagall's Rabbi, with 2 left hands. I would like to end my talk today with a few sentences from Sir John Cornforth who is here today and who offers his thanks for the awarding of the prize on behalf of us both. These sentences summarise our motivation and our experiences: We were born, and we grew up, on opposite sides of the globe. What we have in common is a lifelong curiosity about the shapes, and changes in shape, of entities that we shall never see; and a lifelong conviction that this curiosity will lead us closer to the truth of chemical processes, including the processes of life." And further: "In a world where it is so easy to neglect, deny, corrupt and suppress the truth, the scientist may find his discipline severe. For him, truth is so seldom the sudden light that shows new order and beauty; more often, truth is the uncharted rock that sinks his ship in the dark." Thank you.

Vladimir Prelog (1983)

A Look Back at 118 Semesters of Studying Chemistry (German Presentation)

Vladimir Prelog (1983)

A Look Back at 118 Semesters of Studying Chemistry (German Presentation)

Comment

The way he delivers his first lecture in Lindau, the organic chemist Vladimir Prelog can be seen to personify the dramatic sweeping away of the Austrian monarchy and the establishment of a new European map after WWI. No wonder then that he chooses to catch the interest of the younger part of the audience for the historic development in organic chemistry in the 20th century by describing to them his own personal life story. From Sarajevo (Bosnia) to Zagreb (Croatia), then to Prague (Czechoslovakia), back to Zagreb and finally to Zürich (Switzerland). Since Prelog believes that performing research really means that you are a student, the 118 semesters of the title refer to his life from 1924, when he enters the Czech Institute of Technology up to 1983, when he delivers his lecture at the Lindau meeting. In a book published later, the same year that he passed away at age 92, he actually updates the story to 132 semesters! During his life he met with many inspiring personalities and, as so many other Nobel Laureates, he bears witness to the importance of good teachers, both in school and in Academia. He also considers himself lucky to come to Zagreb as a newly created PhD to be given the task to build up the research activities in organic chemistry with a set of young co-workers. In the next movement, to ETH in Zürich, he mentions in particular three Nobel Laureates in Chemistry who worked there at different times: Leopold Ruzicka (NP 1939), Hermann Staudinger (NP 1953) and Richard Kuhn (NP 1938). It was Ruzicka who had the good idea to invite Prelog to come to ETH in 1941 and from the lecture it seems clear that he never regretted this invitation!

Anders Bárány

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