B.R.S.M. The Battlefield Earth of organic chemistry blogs


BRSM Reviews: Taxol In 10 Minutes


If you're reading this then I reckon you've probably heard of taxol, as it's one of the most talked about synthetic targets of all time. It's a molecule with a fascinating history, from its isolation and structural assignment in 1971, to discovery of its potent activity and interesting mode of action, and the ensuing scrabble to solve the supply problems plaguing its development as a drug.[1] Its rise to success as a billion dollar pharmaceutical was stellar, and is one of my favourite examples of how useful and important synthetic organic chemistry is. Although it's been 5 years since the most recently reported synthesis of taxol, last week's Baran synthesis of taxadiene (following his cyclase-oxidase mimic plan for elaboration of this hydrocarbon into taxol) seems to have again gotten chemists talking excitedly about this target. After overhearing things like 'didn't Nicolaou make it first?', 'there've only been x syntheses so far' (where x is 0-6) and other such misinformation in our office I've decided to take action. Yes, there are already numerous reviews, book chapters and even entire books on this subject, but it seems that a lot of people don't have the time or inclination to read them. So, here's a brief summary of the 7 syntheses published so far, in the order they were completed. Hopefully this'll help put recent developments in perspective.

Filed under: BRSM Reviews, Literature, Total Synthesis | 13,988 views | 8 comments Continue reading

Cycloadditions are great

This is my attempt at answering Rachel Pepling’s call for posts for her blog carnival over at CENtral Science. The theme is 'Your favourite chemical reaction'.

Update: 23/09/11 - removed some of the more egregious grammatical errors.

It only took me a few seconds of thought to answer the question 'What's your favourite chemical reaction', far less than if I'd been asked about my favourite book, meal or album. It's the Diels-Alder cycloaddition, obviously. I reckon I've done well over a hundred of these by now (including three today), and those two names will certainly appear in the title of my PhD thesis. On social media websites I usually list my interests as rock climbing, mountain biking and cycloadditions.[1]

I guess what I like about this reaction, and why it's a mainstay of total synthesis, is that it's a fantastic way to generate stuctural complexity blindingly fast. It can set up to four stereocenters, and you can even take simple achiral precursors and introduce asymmetry catalytically. But, unlike a lot of reactions which are capable of such synthetic leaps forward, it's also generally very  predictable. One of my favourite parts of the history of this reaction is this quote from the seminal paper by Diels and Alder:

"We explicitly reserve for ourselves the application of the reaction developed by us to [natural products synthesis]"[2]

Nice try guys, but the 1300+ papers published in 2010 on this transformation seem to indicate that this request has been largely ignored by the synthetic community. And why not - it's an all round great reaction, probably the hammer and/or duct tape of the total synthesis toolbox. It's also nice that it's named for an advisor and his PhD student, because the people who actually do the chemistry often don't get the credit they deserve. However, despite all of these things I'm not actually going to write about the Diels-Alder reaction here. The reason is that it's just too well known - we even teach it to first year undergraduates. Everyone knows what it is, and how good it is, and I think this carnival is a great opportunity to dredge up some lesser known reactions and hopefully get people thinking about some chemistry that's new to them.

Filed under: Literature, Named reactions | 19,205 views | 16 comments Continue reading