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Target: conolidine

28 May 2011 - Pharma

conolidine synthesis  The opioid conolidine can be extracted from the bark of the plant Tabernaemonta divaricata in a meager 0.00014% yield or synthesised in the laboratory as described by Micalizio et al. in a recent Nature Chemistry publication. This plant has a long history of use in traditional medicine in pain relieve and as related compounds such as pericine have already demonstrated efficiency in this area further investigation into conolidine was warranted.

the reported synthesis consisted of 9 steps starting from 1-(pyridin-3-yl)ethanol and 2-lithio-benzenesulfonyl-indole. Pyridine 1 was protected at nitrogen as 2 by p-methoxybenzylchloride enabling its reduction by sodium borohydride to allyl alcohol 3 and addition of tributylstannyl methyl chloride to allyl ether 4. A Wittig rearrangement with BuLi then gave alkene 5 as a cis-trans mix which had to be separated out by collumn chromatography. The Dess-Martin periodinane then reduced the alcohol group to the aldehyde group in 6, nucleophilic addition with organolithium 7 gave alcohol 8, removing the sulfonyl protecting group with sodium amalgam gave 9, oxidation of the alcohol group (manganese dioxide) gave 10 and PMB removal was accomplished using (the very hazardous) chloroethyl chloroformate to free diamine 11. in the final step formaldehyde was added and the resulting imine intermediate 12 formed conolidine 13 (18% overall yield) in a electrophilic aromatic substitution at the indole ring.

The researchers then also synthesised both enantiomers by enzymatic resolution of intermediate 2 and then subjected all three compounds (racemic, natural (+), (-)) to a round of analgesic screening. Unfortunately the only way to do this is by way of animal testing and if you of the animal-loving kind then please step away from your computer monitor now....

And we are back. The animals (mice) must have suffered (especially those in the control group) in making this research possible because yes, the hot plate test and the warm water tail immersion assay (50°C) are exactly what you think they are. More pain was inflicted by injections of acetic acid and formaline. The preliminary results: conolidine is as good as morphine or better and either enantiomer is more effective than the racemate.

How not to put out a chemical fire

26 May 2011 - Moerdijk again

The authorities are still struggling with the aftermath of the big Moerdijk chemical fire that raged last January. An earlier blog stated two reasons now no longer relevant why water should not have been used to fight the fire. NOS News has interviewed fire-fighting specialists and Chemiepack employees and some interesting conclusions can be drawn Link.

According to the specialists water should never be used with chemical fires for several reasons. Water will just help spreading chemicals and burning chemicals in a certain location, see the clip below for a demonstration. When a fire is allowed to die by itself, it burns hotter and thus cleaner and any smoke will be allowed to rise vertically and to greater height also reducing the environmental impact. Water is only useful in safeguarding surrounding properties. Yet the firemen on duty that night in January kept throwing water directly at the fire for long 10 hours, an estimated total of 55 million liters, before finally resorting to foam. Water is not standard procedure in any fire-fighting handbook according to NOS News and also the Chemiepack employees advised against it. The irony is that this company is now facing a 70 million euro bill for the environmental cleanup.



Fun with boron

21 May 2011 - Pyrotechnics

Sabatini et al. of the Pyrotechnics Technology and Prototyping Division of the US army report a novel way to produce the green light used in fireworks and signals (DOI). The new light is still green but also environmentally friendly. In a traditional formulation you mix barium nitrate, magnesium metal (fuel), a polyester resin (binder) and PVC. Combustion of PVC produces chlorine and then green-burning barium(I) chloride.

This formulation suffers from two disadvantages according to Sabatini: the barium source used may be radioactive and PVC combustion triggers Polychlorinated biphenyl formation. The solution: replace BaCl by the equally metastable green-light emitter boron oxide BO2 which forms by reaction of potassium nitrate and elemental boron Together with a epoxy/polysamide binder this pyrotechnic formulation burns just as green except that it burns too fast. For formulation number three therefore boron carbide was added and in formulation 4 even replaced the elemental boron component. If the US army wasn't green enough already it just got a little bit greener.

Platinum in all shapes and sizes

14 May 2011 - Nanotechnology

platinum nanotech.jpgOne of the main themes in nanotechnology is crystal morphology tinkering. The challenge is to take any inorganic crystalline material and come up with novel shapes at the nanolevel and of course built from the ground up. And in the field of heterogeneous catalysis any new metal catalyst morphology holds the promise of new catalytic activity. A fair share of the work concerns platinum as the next three examples from the recent literature illustrate. And what did you say the reducing agent was?

First up: the research group led by C.B. Murray (DOI). Their idea: as multifaceted crystals tend to grow from the faces with the highest energy and as surfactants can selectively adhere to a particular face lowering this energy, different surfactants can help to grow differently shaped nanocrystals. The advantage of using peptides as the surfactant component is that they can be tailored by their specific monomer sequence.

In their recipe chloroplatinic acid is reduced by two reducing agents: sodium borohydride and ascorbic acid. The first one (fast) is added as a single-shot and will initiate platinum nucleation as truncated tetrahedron. The second one takes it slower and reduction is continued with platinum atoms growing from the crystal face lowest in energy depending on what surfactant is used. The peptide Ac-Thr-Leu-Thr-Thr-Leu-ThrAsn-CONH2 for example produces cubes and Ac-Ser-Ser-Phe-Pro-Gln-Pro-Asn-CONH2 produces tetrahedrons. These peptides were selected from a large commercially available chemical library of peptides. Procedural details are fuzzy (journal editors: pay attention!) but the library (how big?) was exposed somehow to Pt cubes and octahedrons sythesised from established methods and in some manner the relative peptide affinity for either shapes was measured at some stage involving infecting Escherichia coli (no, the supplementary information did not help).

Another novel development is the platinum nanolawn as recently described by Shen et al (DOI). To create one apparently all you have to do is heat a solution of Na2Pt(OH)6 in water (chloroplatinic acid does not work) at 300°C on a titanium oxide surface. The resulting lawn density is 80 nanowires per 100 square micron, with wires diameter 34 nanometer and height up to 6 micron. Shen et al. claim platinum is reduced by electrons generated from TiO2, photocatalytically at first and then thermally. This is somewhat confusing since the whole procedure never mentions a light source.

In the meanwhile Cavaliere et al. (DOI) have been busy doing the opposite: TiO2 nanofibers covered by platinum. Take a solution of PVP (carrier polymer), Pt(II) 2,4-pentanedionate, titanium(IV)isopropoxide, niobium ethoxide (Nb doping required) and make fiber by electrospinning. Heating to 500°C removes the carrier polymer and deposits Pt nanoparticles as little nanobugs. Again the hunt was on for the nature of the reducing agent, trace alcohol left or carbon monoxide from polymer decomposition were suggested.

Dutch chemistry departments: we are fantastic!

6 May 2011 - PR

The Dutch University chemical departments have hired QANU (Quality Assurance Netherlands Universities) for an external assessment. It must have cost them some money but in return they now have 146 pages of gloating references to impress their friends or more importantly the funding bureaucrats. And do not think the assessment involved any objective data gathering and statistical data analysis: the report is 100% figure-free. Instead a group of scientists from abroad was invited to give their personal opinion. Quality was then ranked on a scale from 1 to 5 with 1 unsatisfactory and 5 excellent. Main result: an average 4.2 points, meaning the overall research is nationally leading and competitive internationally in a particular field.

Here are some quotes: On a University of Groningen research group: The leadership is overall quite dynamic , on a VU Amsterdam research group : the group currently has a strong presence in analytical chemistry, and on a Leiden University group : The quality of this group is excellent. These statements appear rather meaningless if based on the personal opinion of a small number of peers. The assessment is also based on a 10-year period which is long if a lot of emphasis is given to leadership skills of the present scientific management. Also a lot of weight is given to relevance of scientific output to a particular field. The relevance of that field in the scope of general scientific exploration is not assessed. And by the way: Dutch universities are already assessed on a regular basis by the Ministry of Education with relevance to educational accreditation, all the more reason this report should not have been written.

The technical universities resisted the cheap PR temptation and are not included in the assessment. Must have wasted their budgets on silly things such as staff & equipment.