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Total Syntheses of Cyanthiwigins B, F, and G
In 2001 Martin reported a biogenetically inspired synthesis of strychnine. Hydroxyakuammicine (41) was selected as a late-stage intermediate, because its 3-step elaboration to strychnine was known from the Overman synthesis (). Martin planned to mimic the biogenesis of Strychnos alkaloids () by forming hydroxyakuammicine from deformylgeissoschizine derivative 71 by an oxidative rearrangement cascade. Intermediate 71 was seen deriving from an intramolecular hetero Diels–Alder reaction of aldehyde 72, which in turn would arise by tandem acylation/vinylogous Mannich reaction of dihydro azacarbazole 73.
That, coupled with the fact that no-one had ever used the meta-photocycloaddition reaction in total synthesis before at all; it had pretty much remained an academic curiosity since its accidental discovery by Bryce-Smith using the finest British sunlight at the University of Reading!
Synthesis of Strychnine by Larry E. Overman (1993)
I actually enjoyed O.L. Chapman’s total synthesis of carpanone, both studying and performing it. Quite a short and cute synthesis, in my opinion.
Has anyone else noticed the variety of arrows used in retrosyntheses in the literature? A lot of people seem to be using closed arrows these days (for a recent example from someone who should know better, see the abstract of Baran's from last month), rather than the more traditional open ended ones (). I can't easily give an example of the incorrect kind above, because as far as I can tell there isn't a character for it in any font. That's because, as far as I know, it doesn't mean anything. The open arrow, on the other hand, predates the concept of retrosynthesis by a long way, as it's the logical operator for the implication relation. So A B means that the presence of A implies B. Which kind of makes sense. Eager to find a supportive quote from E. J. Corey, who coined the term retrosynthesis, I dug out my copy of The Logic of Chemical Synthesis, and was pleased to find the following:
Total Synthesis of Strychnine: L. E. Overman's Approach
The Shibasaki synthesis ((-) chiral, 2002) was a second published method in strychnine total synthesis using an . 1 was reacted with 2 in an using to form chiral diester 3. It's group was protected as an (2-ethyl-2-methyl-1,3-dioxolane, ) and a carboxyl group was removed (, 140 °C) in monoester 4. A C2 fragment was added as 5 to form 6 using . The ketone was then reduced to the alcohol (, ) and then water was (, ) to form 7. After reduction () to the alcohol and its protection (TIPSOTf, ), the acetal group was removed (catalytic ) in ketone 8. 9 was then formed by . The conversion to alcohol 10 was accomplished via a using , to 11 (, ) was followed by a (, , ) incorporating unit 12. Alcohol 13 was formed after protection (SEMCl,i-Pr2NEt) and TIPS removal ().
Lessons Learned in Strategy and Tactics in Total Synthesis Strychnine thrillers beyond Agatha Christie: The complex indole alkaloid strychnine has engaged the chemical community since the 19th century.
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Total synthesis of Strychnine: - UW-Madison Chemistry
This week’s group meeting’s talk on ‘Strategies in Synthetic Planning’ raised a number of interesting points for discussion, but I wanted to put just one to my readers and the online synthetic community: what’s your favourite total synthesis?
Total synthesis of Strychnine: Reference: Knight, S
A couple of weeks ago the MacMillan group published a remarkable paper reporting the asymmetric synthesis of six natural products, from three different alkaloid families. I only noticed total syntheses coming out of the MacMillan lab two or three years ago, but now they're something I always find myself getting excited over, and this is no exception.
THE TOTAL SYNTHESIS OF STRYCHNINE - Journal of …
MacMillan contends at the start of the paper, and he's not the first, that given enough effort, money, and time it's now possible to make at least a few milligrams of almost any known natural product. Just look at Kishi's synthesis, for example, or the ongoing Nicolaou efforts towards sporadically appearing in JACS. We all know that it's when you need to make large amounts of any complex molecule (even grams), that your troubles really begin. Another thing that takes a huge amount of effort using conventional chemistry is the preparation of libraries of natural products (and their analogues) for biological testing.
THE TOTAL SYNTHESIS OF STRYCHNINE
Obviously, Nature is much more better at the construction of complex molecules, thanks largely to its peerless enzyme catalysts and amazing use of cascade reactions. Another thing that makes Nature's approach very efficient is that it tends to produce a number of natural products from a single intermediate, giving rise to families of compounds. The broadest example I can think of is the use of and to produce the s, to which entire series of books have been dedicated, but there are also many smaller groups of natural products thought to share a common biosynthetic precursor. Chemists, on the other hand, traditionally just choose one or two targets, although we are getting a bit better at this, and 'general methods' for the synthesis of families of natural products are now not uncommon. While many different definitions of 'the ideal synthesis' and 'efficiency' have been offered, T. Hud. stated a few years back what he thought was the paragon of modern synthesis:
Total synthesis of (−)-strychnine is described
"The highest possible level of craft requires the synthesis of an entire class of natural products by a unified approach resembling, in principle, their biogenesis. All members of a specific class (as well as all of their possible diastereomers) should be attained in an enantiodivergent fashion as single entities"
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