Hyperspeed Hyperforin

Kudos to the Maimone group (UC-Berkeley), who have published in JACS ASAP what seems to be the speediest synthesis of a hyperforin on record - just ten steps!

Perhaps this lends more credence to the Eastgate's "current complexity" index, which measures synthetic simplification over time thanks to improved methods. But who would have guessed that in just five short years this synthesis would telescope from 50 steps down to just 10? Strychnine, albeit a very different challenge, took nearly 60 years to simplify from 30 steps down to Vanderwal's highly-convergent six.

For Chemists: Steps of interest include a highly-oxidized [4+2] diketene cycloaddition, a iodoacetate-promoted ring expansion, and a highly modular synthesis widely amenable to analogue production.

For Everyone Else: Why should I care that this ungainly-looking molecule was made faster than before? First, hyperforin and related secondary metabolites (natural products produced by living organisms) isolated from famous folk remedy St. John's wort suggest new avenues for the treatment of of malaria and certain forms of depression. Second, if chemists can make variations on this molecule in roughly one-fifth the time, we can expect a venturesome start-up somewhere to begin fleshing out the SAR (what chemical modifications product what activities?) in record time.

"But...This Synthesis Goes Up to Eleven!"

Have you had fun reading through all the hilarious send-ups on the Twitter hashtag #HonestChemTitles? This tag tries to dig down to the subtext behind highfalutin words and strange symbols, uncovering the hidden motivations behind scientific papers. And...it's a hoot.

Remember the tweet that kicked off this brouhaha? A harmless convergent synthesis of some Lycopodium alkaloids. Kudos to @AlexFGoldberg for highlighting the authors' rather overblown title:

Classic children's literature;
my first exposure to superlatives

Amazingly, that 10-word title is 30% superlatives and 30% chemistry, with a smattering of conjunctions and articles to connect them. As others pointed out, how do you measure "elegantness," anyway? And when does a total synthesis cross the line from concise to exceedingly so; can anything more than a one-stepper be really succinct?

Sort through the paper with a grammarian's fine-toothed comb; one wonders if it wasn't run through some sort of excitement thesaurus, perhaps to get people really stoked about these routes.

Here's all the intense words and expressions I found:

Diverse
Useful
Unique
Challenging
Efficient
Complete
Direct
Achieved
Accomplished
Value
Exceedingly concise and convergent
Attractive

...and that's just in the first paragraph, folks.

Nigel Tufnel (Christopher Guest), ca. 1984

Honest opinion? Aside from the goofy title and superlatives liberally sprinkled into the text, the chemistry seems solid. Nothing's breathtaking - setting an early quaternary center through steric control is nice, and telescoping the three steps before the desired tetracyclic dione works well - but there's no "killer reaction" for me in this paper. The NMRs are clean, and the synthesis represents a decent improvement over existing methods.


Thus, I'd like to accept this publication into the "Spinal Tap Synthesis" category, so-named for the hard rock auteurs profiled in 1984's This is Spinal Tap, the tongue-in-cheek rock mockumentary. If you've never watched the movie, I won't spoil it, but I highly recommend the sequence in the middle where Nigel Tufnel, the vapid, misunderstood lead guitarist, obsesses over a "special" amp he designed that "goes to 11."

Fits this paper to a T.

(Please) Make More Molecules using Light!

Update (6/29) - Commenters chime in with some notables I'd mistakenly left off the list. I'll append their molecules to the end of this post (vide infra)...

I'm officially calling it: Photoredox catalysis = the new "it reaction" for organic chemistry.

Like many before it - iron catalysis, the gold rush, anything palladium, organocatalysis - photoredox catalysis is now appearing in my RSS feed on a near-hourly basis. We're in the early days of an exciting field; I've noticed more methodology papers and mechanistic studies lately. Assuming you start with a suitable aryl halide, diazonium, or carboxylic acid, the synthetic toolkit of single-electron catalysis seems virtually limitless.

Which begs the question . . .where are all the photoredox total syntheses?

Three examples of recent total syntheses that capitalize
on photoredox catalysis (bonds in red)

SciFinder: "photoredox total synthesis?"
7 hits.

How about "light-mediated total synthesis?"
7 more.

One more try: "photoredox natural products?"
7 hits.

Most of these hits actually lead to conference abstracts, not individual manuscripts. Props to the Stephenson group (Michigan), who leads the charge with syntheses of aspidosperma alkaloids and gliocladin C. Based on SciFinder results, I'd include the MacMillan synthesis of Lyrica, and Lei's isoquinoline syntheses from JOC.

Readers, what am I missing? A pivotal review or book? A group whose research is at the forefront of solar-powered natural product production? Perhaps a major non-English journal article? Any examples where a venerable old lion of total synthesis utilized a photoredox reaction alongside their Diels-Alders and aldol reactions?

For such a large-upside field, it sure seems quiet out there.
--
Update: Molecules made with photoredox catalysis, as suggested by my beloved commenters:

Overman, (-)-aplyviolene, Ru(bpy)3
MacMillan, fenofibrate (OK, not a np), Ni(II), Ir(III)
MacMillan, (-)-burshernin, Ru(bpy)3
Nicewicz, methylenolactocin and Protolichesterinic Acid, acridinium
Nicewicz, magnosalin + pellucidin A
Yoon, heitziamide A, Ru(bpz)3
Yoon, epiraikovenal, Ir(III)
Chen + Baran, sceptrin, Ir(ppz)3
Chen, nakamuric acid, Ir(ppy)3
Lawrence / Sherburn, endiandric acid A, kingianins A,D,F, kingianic acid E, Ru(bpy)3
Carreira, (+)-Daphmanidin E, Co-diimine (method here)

More?

Oxidase Toolkit: C-H Azidation

Do you ever stare at your late-stage molecules, thinking "They're almost perfect, but I really wish I could add an amine right over there." Thanks to a new reaction, you might soon be able to.

Reporting in Nature, John Hartwig and coworkers have cracked the case: a mixture of iron (II), a tridentate nitrogen ligand, and a modified Togni reagent Zhdankin reagent reliably functionalize tertiary C-H bonds with an azide(N₃ group). The selectivity, yield, and mild conditions match pretty well with White's C-H oxidation, which utilized a similar catalytic manifold.

Hartwig's initial targets for this new reaction include two modified steroids and a gibberellic acid derivative. Sadly, precious few heteroatoms exist in these molecules to gum up the ironworks, but I'm certain they'll address that in the full paper. I'd especially like to point readers to Figure 3, in which the group shows subsequent transformations: heterocycle formation, amine reduction, chemical ligation, and capping with fluorescent tags.

These two reactions together, along with a variety of C-H halogenations and sulfidations, seem to support the growing "oxidase phase" approach to total synthesis. One could imagine that, in a few years, a naked carbon scaffold could be suitably decorated with O, N, S, or X at positions of the scientists' choosing. Wow.

Friday Fun - Maitotoxin Watch

For those keeping tabs on K.C. Nicolaou's potential career capstone, the group has published another fragment (QRSTUVWXYZA') of the ladder polyether maitotoxin. By my count (and thanks to their handy graphic, below), they've now formed 30 of the 32 requisite rings, meaning we'll likely see a completed total synthesis in the next few years.*

Top: Maitotoxin
Bottom: Previously disclosed fragments
Source: Nicolaou et.al. | JACS 2014 ASAP

When Nicolaou's group announced the move to Rice, one of my first thoughts was "who gets to personally chaperone the maitotoxin fragments to their new home?" I'm picturing combination-locked black suitcases handcuffed to postdocs' wrists, but perhaps the samples just went in the back of a U-Haul truck with all the other lab equipment.

Happy Friday,

See Arr Oh

--
*Assuming they can work out the ring fusion and selective sulfate chemistry - not trivial tasks by any means!

Bruceollines: Short and Sweet

You can't put your finger on it, but sometimes you just feel compelled to read a paper. This one, from Org. Lett. ASAP, scratched all the usual itches: protecting-group free total synthesis (check), traditional medicine (check), tropical diseases (check), and cool off-the-shelf reagents (check).

I must admit, Gordon Gribble's name at the top caught my attention, but his co-authors hail from the University of the West Indies, a school I've always been curious about.*

The goal? Fast, selective production of bruceollines, medicinal compounds isolated from the roots of a Chinese shrub. The authors initially try to assemble the common indole (the 6-5 aromatic ring) core of the bruceolline family using Fischer conditions, but the starting materials have other ideas and form non-productive intermediates. Starting over, palladium catalysis proceeds smoothly, then relatively gentle oxidation (DDQ) produces the fully oxidized bruceolline E (see picture).

To access the final compound, Gribble & Co. must reduce just one of E's two ketones. The authors attempt borane reductions, but the "usual suspects" (CBS, Alpine) fail miserably. Optimization with (+)-DIP-Cl produces the final bruceolline J in high yield and ee. To make the unnatural enantiomer, the authors turn to a personal favorite: Baker's yeast, more commonly found in breads than labs. After 14 days in a warm, sweet slurry, the wee beasties return ent-bruceolline J in 98% ee.

The synthesis, only 4 short steps, should open the door to develop new antimalarial compounds.


*First, the Hawaii paradox - recruiting high-end, serious grad students to work 4-6 years in a tropical paradise. How does that work? And how do shipping delays from the mainland impact project selection? I can imagine that protecting group-free, relatively robust chemistry would have to be the norm, to survive storms, delays, humidity, etc.

Scalable Ingenol? Phil Strikes Again!

Update: Want the inside scoop? Check out Open Flask!

I'm officially declaring it: Every 6-7 months, we should expect another huge molecule to fall to Phil & Co:

May 2011: Cortistatin
November 2011: Taxane Cores
May 2012: Ten Meroterpenoids.
December 2012: Ouabagenin

July 2013: Seen the latest* over at ScienceExpress? I think this scheme sums the whole thing up quite nicely:

And that's why it's in Science, kids...
Source: Baran Group | ScienceExpress

Ingenol falls! LEO Pharma, in collaboration with Scripps, may soon make gram-scale batches of ingenol analogs - something that used to take entire groups years to make. This paper cheers from so many different bleachers, I can't even count 'em all:

Total synthesis accesses trace plant metabolite!

Investment in basic research reaps huge Pharma dividends!

Imitating nature makes stitching together complex terpenes look easy!

Enzymes, Schmenzymes...

This paper really does have something for everyone. A volatile intermediate gumming up the works. A surprise crystallization. X-Ray structures. Some allenic Pauson-Khand reactions. A low-temp vinylogous pinacol rearrangement. Even some C-H activation / oxidation tossed in at the end.

If you want some more ingenol goodies, head on over to Chemistry World's fantastic write-up.
And, of course, join me on PhilWatch somewhere around January 2014...

*Thanks again to Brandon for a copy.

Get it Funded! (A Game)

Last night, intrepid C&EN reporter Dr. Dre, err, Dr. Drahl, sent over another challenge from NOS2013:

I think Jerry Berson talked w/me re funding influencing field flux. So what's gonna happen to totsyn?
— Carmen Drahl (@carmendrahl) June 27, 2013

Let's reword that: How will changes in funding affect total synthesis, the study of assembling complex natural products from simple commercial chemicals?

Now, this isn't the first time folks have declared the synthetic field to be on death's door. Hardly. So, I answered the way I always do, which has kept the field alive and kicking long past Woodward:

@carmendrahl @2014RMC @ChemProfCramer TotSyn will survive - it'll just dress itself in new clothes for new funding opps #SameOldStory
— See Arr Oh (@SeeArrOh) June 27, 2013

Chemjobber, always one for a savvy one-liner, immediately jumped on board:

.@SeeArrOh "Towards the enantioselective nanodelivery of 56-desoxymaitotoxin" @carmendrahl @2014RMC @ChemProfCramer
— Chemjobber (@Chemjobber) June 27, 2013

Nyuk nyuk nyuk. OK, wise guy, I've got a few more, then . . .

"Reversible carbon dioxide capture using lycopodium alkaloid analogs"

"Pentacene-functionalized steroids for solar panels"

"Origin of Life: The Gliotoxin Hypothesis"

"Analysis of 10^5 novel secondary metabolites in the human gut microbiome"

OK, Readers, I'm sure you can do better. Leave me some gut-shakers and knee-slappers in the comments section!

The Pterodactyl Flies Again

I'll admit it: I was a bit bummed out to read B.R.S.M.'s tweet regarding Totally Synthetic's untimely demise:

As a young pup, I cut my teeth in a few guest posts over at Paul's place. Since I saw a sexy, streamlined version of one molecule go by in Org. Lett. last week, I decided to do a (memorial? celebratory?) post in true Tot Syn style.

Folks who've read the other syntheses might agree with me that the trigonoliimines, as drawn by Tambar, resemble a terrifying pterodactyl:

Respectfully stolen from Tot Syn

Both Tambar and Movassaghi aimed for asymmetric syntheses, and started from a [2,2] fusion point between differentially-functionalized tryps. They're aiming to make the whole lot (Trig A-C), so this semi-biosynthetic approach makes sense. But Hao's latest paper sets its sights squarely on (all together now!) the (6/5/7/5/6/6) core of Trig A - sadly, a much "flatter" molecule with less 'dinosaur' character. But, the target still shows moderate antiviral activity, so the group reasons a shortened synthesis may expedite analog generation.

Hao aims to use two fairly well-known reactions to join his tryptamines: a modified Strecker, followed by a Houben-Hoesch cyclization. First, the group pops open a methoxylated, phthalamide-protected Trp precursor using CuCl under oxidative conditions (the 'cool' kids use blue LEDs now). Now they've set the stage for the really short racemic synthesis:

Initial TMS-promoted imine condensation with the aryl ketone sets up a CN alkylation, which cyclizes on the nearby formamide (probably through an isonitrile). Now here comes a 7-membered Houben-Hoesch ring closure, which they perform in a one-pot prep due to instability of the methoxy-Strecker intermediate. Basic workup, followed by hydrazine deprotection / cyclization, produces Trigonoliimine A, in a respectable 35% yield (4 steps, 3 pots).

Godspeed Dr. Docherty, wherever you are...

Update: Neil posits that Paul is still alive and well, and writing for Chemistry World.