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Work on sponges: setting up underwater labs


Marine chemistry: discovering new sterols
Carl Djerassi Scientist
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All of these physical methods, though, enabled me to examine an area which is much more difficult, because natural products chemistry, which has the longest history in organic chemistry, involves terrestrial things, and for obvious reasons, because... things that you could find easily, and in general even in areas that are accessible, and of course, the more esoteric the areas are the more likely, geographically, you are likely to find newer things, and in tropical plants... and plants are easier than animals. So the bulk of natural products chemistry is overwhelmingly plant chemistry, and then animal chemistry, and more recently also insect chemistry. But when you get to the ocean, there is of course an awful lot more in the ocean than anywhere else, but we don’t get to it. First of all, because it was not accessible until fairly recently, you know, until even diving equipment, even scuba diving was invented, which was really, only you know, the last century, and... but even that, the... only depths to, let’s say, 150ft or so, conveniently for really collecting. If you want to go further down it’s submarines, and then you may even get into depths where you have unmanned submarines, but these are things that have only been developed quite recently. And the things that you can then collect are, first of all, very few things, very little, and sometimes very rare. And it is marine chemistry that I became interested in, in the late 1970s, early 1980s, and probably for the last 20... the last 15 years of my chemical life... I closed my lab in 1992, more and more the focus of the natural products part of the research was done on marine animals.

It was then a fascinating completion of a circle, because I focused particularly on steroids, and particularly on sterols, things like cholesterol, and so on, and that was an area of steroid chemistry that I, and most other steroid chemists thought had been exhausted, almost exhausted. There are very few new terrestrial sterols that you isolate. Cholesterol is the mother substance, and it is a constituent of cells. It is not only the raw material out of which we make our hormones, through chemical transformation in the body, but cholesterol as such, without any further modification, is a key constituent of all cell membranes, and you cannot have a cell without a cell membrane, or it wouldn’t be one, and the cell membranes consist of two things basically, phospholipids, and then cholesterol. And so the question is why... what is the magic role of cholesterol, and a lot of work has been done on this, thousands of papers, and it’s one of the key areas in biology... structural biology, and etc, even evolutional biology, if you wish. And what happened is, working on marine animals, I suddenly discovered that they contain sterols, but of a very unusual nature, in that only one part of it there, not the part of... and here I can show you some chemical structures, because I’m sure I have it in here. Well, here just the tail... yeah. See it right here, here’s the structure that basically is cholesterol, except it has a double bond here, but that would be cholesterol, and has this side chain, each of the carbon atom... R means... R is not an atom; it just means here there could be other things as well. R is equal to hydrogen, methyl, ethyl, and so on. But if you forget the R and put in a double bond, that’s cholesterol, and cholesterol is present in all of the cells. Now, what is very important is this thing here, because this has to occupy space in the cell membrane, and modifications of this R in ordinary mammalian cell membranes, and so on, and makes them poorer, because one can make artificial cell membranes, so one knows cholesterol is the ideal... evolutionarily the ideal situation.

Suddenly we discovered in marine animals, and this is just this part, just the side chain, things like this, where each of these circles and other methyl groups, so you see this bizarre thing, you see methyl grouped all around, in places that we never anticipated, it was just a... I mean, and then even more bizarre were the things that had these rings, three membered rings, which are cyclopropanes, or three membered rings for the double bond, which are called cyclopropenes, and there are practically no natural occurring cyclopropenes anywhere in nature, very, very few. So all these bizarre things were suddenly discovered, and we literally, as I said, there were hundreds of new sterols at a time when you’d think there weren’t any more sterols, and all from marine organisms. And that got us going on an awful lot of things, but we started first with sponges, but then with other marine animals, and that we really only could do because we developed these techniques, and in particular mass spectrometry, because sometimes you had so little material that you couldn’t even see it, and yet we could determine the structure through just two things, namely, mass spectrometry and NMR, nuclear magnetic resonance, and then we eventually synthesised them to confirm that they actually existed.

Austrian-American Carl Djerassi (1923-2015) was best known for his work on the synthesis of the steroid cortisone and then of a progesterone derivative that was the basis of the first contraceptive pill. He wrote a number of books, plays and poems, in the process inventing a new genre, 'science-in-fiction', illustrated by the novel 'Cantor's Dilemma' which explores ethics in science.

Listeners: Tamara Tracz

Tamara Tracz is a writer and filmmaker based in London.

Tags: Sterols, cholesterol, phospholipid, Cyclopropane, Cyclopropene

Duration: 5 minutes, 58 seconds

Date story recorded: September 2005

Date story went live: 24 January 2008