#Retrotime - Cycloheximide

Cycloheximide 1 is a cheeky number that is worth a mention.  It is a tool compound with a proven track record of actually being useful, with its years of use in cellular biology.  Regarding retro, I have included a brief synthesis at the end, so no peeking as it will tarnish your retrosynthetic blank canvas.

Cycloheximide was isolated from the bacterium of Streptomyces griseus and has been used in a variety of applications including as a fungicide, rodent repellent and medicinal, although the latter has stagnated as it is a potent inhibitor of eukaryotic protein synthesis.

Cycloheximide is closely related to other glutarmide ring containing fungal metabolites, which have been examined for their biological effects.  It had been known that cyclohexamide inhibits the translation of mRNA into proteins, but this paper was able to further pin point cycloheximide’s mode of action.  Cycloheximide stops deactylased RNAs from leaving the E site of the ribosome and therefore halting the translational process.

Cyclohexamide’s biological effects have been of great value to cellular biologists whilst investigating protein targets.  For example the addition of cyclohexamide during an experiment can help determine the protein’s half life.  Cyclohexamide’s effects are specific to cytosolic protein synthesis and do not affect mitochondrial protein synthesis.  Cyclohexamide’s mode of action has been further exploited to examine the full extent of protein expression in a cell through ribosome profiling. The technique isolates mRNA which are being translated in the ribosome and produces a global picture of the cells activites. Briefly, 1) Cycloheximide imobilises mRNA bound to ribosome, 2) Complexes isolated (sucrose gradient), 3) Produce cDNA by reverse transcription 4) Sequence DNA – produce translational profile, Cyclohexamide is inexpensive and works rapidly, Its effects are rapidly reversed by simply removing it from the culture medium.

STOP! below is a route to the chemical synthesis of the target molecule. It's time to put the internet down and pick up a pen and paper and get scribbling.

Below is a diastereoselective synthesis from the 60s by Johnson et al

Synthesis of a key intermediate - Glutarimide-3-acetic acid

Completion

The paper is a very honest account of their synthesis, which is very refreshing.  For me, the epimerisation of the C2 methyl upon enamine formation and the reduction of the dicarbonyl were non-obvious.  Therefore my retro went down a less than satisfactory route and probably would have resulted in a messy aldol bringing the two fragments together.  I also would have done a lot more columning than these guys, who only seemed satisfied with pure colourless product crystals crashing out at each desired stage.