OC tidbits #7

Mose et al. (Jørgensen lab) [Nature Chemistry]

There are whole bunch of messy electrocyclic reactions in the paper and nice projections explaining diastereoselectivity. They made me nostalgic about reading OC texbooks.

mose_et_al

Hugelshofer and Magauer [JACS]

Want something even cooler, here’s a dyotropic reaction! Characterizing the side-products must have been a lot of fun. As well as monitoring the progress (the major undesired product had the same Rf as the starting material, and good luck with crude NMR). Heads up from amphoteros.

hugelshofer

Hall, Roche, and West [OL]

Was this reversible photo-switch discovered by accidentally shining a wrong UV lamp onto the final product?  The authors say it was expected. [Note: UVA = 350 nm; UVC = 254 nm]. TOC graphic:

ol-2016-03689z_0005

Chen et al. (Yu lab) [ACIE]

OK, enough electrocyclic reactions. Here’s some C-H activation work from Jin-Quan Yu lab. From [phthalimide-protected] alanine to [phthalimide-protected] substituted phenylalanines in one step! The conditions are somewhat peculiar though. A lot of silver (and quite a lot of palladium) was consumed for this to happen.

yu

Shi, Jiang, and Tian [JOC]

Tellurium is not very popular among chemists (and even less among anybody else for that matter), so each successful use of it is worth attention. The authors of this paper managed to find an application for sodium hydrotelluride. As an excuse they wrote this last sentence of discussion: ‘Reduction of the α-azido ketone 31 with PPh3, as in the Staudinger reduction, followed by stirring in air could not deliver 34 in our hands.’
tellurium
Another unusual thing in the paper is the open call for collaborations: ‘For now, gram scale of 30 and more than 100 mg of 34 [12,12′-azo-13,13′-diepi-Ritterazine N] are available for any interested collaborators.’ I felt obliged to spread the word.

Remote cell reprogramming for diabetes treatment

Since I’m not that long in diabetes business, two new Cell papers from Collombat and Kubicek labs looked quite sensational for me. Both are the products of multi-centered collaborations, and both report regeneration of insulin-producing beta-cells in vivo with small molecules.

As I learned from introductions, reprogramming of pancreatic alpha cells (glucagon-secreting) into beta cells is a sort of a Holy Grail of regenerative medicine for diabetes treatment. Naturally, first attempts to reprogramming were performed with aid of transcription factors. But pretty soon small molecules kicked in. These were kinase inhibitors and chromatin-altering probes from Stuart Schreiber lab, resveratrol (of course!), and peptide hormone betatrophin. OK, the last one doesn’t count, and it’s not a small molecule anyway. What’s unusual about the latest Cell papers, is that they describe reprogramming by small molecules acting pretty high upstream from direct gene regulation [1]. Both papers involve messing with GABAA receptor signaling.

Let’s start with the Kubicek lab paper, which found that common (yet Nobel-winning) malaria drug, artemisinin, can make pancreatic alpha cells to secret insulin. The authors identified artemisinin and its metabolite dehydroartemisinin from a library of 280 existing drugs [2]. After they found that the drugs induce insulin secretion, they identified gephyrin as the most likely target. Then, via electrophysiology and a series of inhibitory tests, they linked gephyrin-mediated activity to GABAA receptor signaling. Known agonists of GABAA, however, didn’t increase insulin secretion as much as artemisinin (after 72 h treatment of cells). The drug then increased mass of beta cells islets in zebrafish, healthy and diabetic mice (while reducing basal glucose level in the last ones). Finally, it altered gene expression in human alpha cells and increased insulin secretion by the islets. Frankly, the figure 7A-C, which is supposed to convince in the last effect, raises some questions as data look cherry-picked from different donors. But authors do address that by briefly mentioning donor-to-donor variability. And it’s not surprising at n = 6 sample size.

artemisiningaba

The paper from Collombat lab branches from the screening results of the first one. Once researchers noticed that activation of GABA signaling correlates with alpha-to-beta conversion, they thought “why not injecting plain ol’ GABA into mice?” And miraculously this simple idea worked. Just look at the jaw-dropping figures 1B-D! Figure S7C,G (below) can somewhat give you the feeling, but go check out the main paper, you won’t be disappointed.

insulin
Figure S7 fragment showing increase in insulin-producing cells from rat pancreas. I assume scale bars, if they were present, would be equal (Ben-Othman et al paper)

Here are the main results: daily injections of GABA at 250 μg/kg over three months convert pancreatic alpha cells into beta. But what’s even more exciting is that the new alpha cells are continuously being produced to compensate for those that were converted into beta! They even caught small fraction of cells in some transitional state, where they secret both glucagon and insulin. I particularly liked the discussion section where authors warn that before you, all excited, rush to inject diabetic patients with GABA think why there’s not enough beta cells in the first place. Yes, it is patient’s immune system that attacks her own beta cells. So before this approach makes into clinic one needs to figure out that autoimmune component of type 1 diabetes.

In a sum we have two great papers with rock-solid mouse data and some exciting preliminary results in human beta cells. Let’s see where it will end up. Regardless of the future success, isn’t it amazing how small, simple, and seemingly well-known molecules like GABA (and artemisinin for that matter) can upturn human cells identity?


[1] OK, authors do not strictly claim reprogramming as the identity of cells doesn’t change completely from alpha to beta, but their secretory activity is definitely flipped.

[2] Side note: check out this sexy acoustic liquid handler they used.

 

My first Shiny app: fitting sigmoid curves

Since the grad school I have been using R for data analysis and (mainly) for preparation of nice plots. As with LaTeX, it was a pretty steep learning curve. But after a year or so I managed to become comfortable with writing a new script for each new experiment. After some time, however, I started feeling that it wasn’t enough. Many experiments were almost identical, so breeding 99%-similar scripts didn’t seem to be an efficient way of handling data. That’s when I first started to think about making ‘reusable’ apps for specific purposes. Continue reading “My first Shiny app: fitting sigmoid curves”

β2AR: old horse’s new tricks

It’s almost four years since the Nobel prize in chemistry went to Brian Kobilka and Robert Lefkowitz for their contribution in our understanding of G protein-coupled receptor (GPCR) signaling. They did their most exciting work by studying β2 adrenergic receptor (β2AR). Yet, despite the titanic efforts, the receptor still holds lots of secrets from us. Continue reading “β2AR: old horse’s new tricks”

OC tidbits #6

Nicolaou et al. (JACS)

Nicolaou et al. does some medicinal chemistry on prostaglandins. Take a look at this Bobbit‘s salt protocol for deprotection/oxidation combo. It seems like they overload the reaction, compared to the original paper, which used 3 equivalents of the oxidant, but who cares if it works?

Bobbit_Nicolaou

Moragas et al (ACIE)

Unprecedented (c) sigmatropic rearrangement of aziridines into sulfoximines.

Stockman_rearrangement

And De Kimpe’s rearrangement for comparison.

deKimpe_rearrangement

Li et al (ACIE)

I’m not sure I would buy the proposed mechanism for the conversion below. The authors skip ‘−H2‘ step and get away with it by simply writing “the imine intermediate 44 […] underwent tautomerization and a key decarboxylation to generate 45 with higher oxidation state.” Something else is clearly happening under that −CO2 arrow and it’s not mere tautomerization.

Hamigerans-proposed-numbers

Wappes et al (ACIE)

So similar, yet so different halogens. I guess, NaF won’t give anything useful under these conditions.

halogens-NHTs

 

No fail no gain

While astronomers recently have been celebrating great discoveries (gravitational waves from colliding black holes keep rolling), at the opposite end of matter size ruler things don’t look as brightly. For instance, the search for ‘sterile’ neutrinos didn’t spot anything, despite the IceCube, a massive 2-km long neutrino detector buried in the Antarctic ice.

Continue reading “No fail no gain”

Skepticism about synaptic nanocolumns

Couple of days ago I’ve come across a recent paper in Nature with quite an eyebrow-raising title “A trans-synaptic nanocolumn aligns neurotransmitter release to receptors“. The title made me think as if the authors have observed hitherto unknown structures in the synaptic cleft. That would be quite a sensation! But then this sentence comes in the abstract:

These presynaptic RIM nanoclusters closely align with concentrated postsynaptic receptors and scaffolding proteins4, 5, 6, suggesting the existence of a trans-synaptic molecular ‘nanocolumn’.

Now it looked like they propose some kind of neuroscience equivalent of dark matter. You know, something that nobody knows what it is, but that certainly must be there, otherwise there’s no explanation to what we see. Continue reading “Skepticism about synaptic nanocolumns”