When most chemists think about catalysis, they probably don’t think of vegetables. But apparently they should. Wenju Bai and colleagues at AbbVie used purple carrots to reduce a group of nitrogen-containing heteroaromatic ketones and got compounds out the other end more easily than metallic catalysts can (ACS Med. Chem. Lett. 2023, DOI: 10.1021/acsmedchemlett.3c00114).
Scientists have known for a while that there’s an enzyme in fruits and vegetables that can perform bioreductions to make chiral compounds, Bai says. But there are limitations to these reactions. They have to run for 1–2 weeks, have low conversion rates, and don’t make highly enantioselective products, he says. “Previously, people have proved that carrots did a good job compared to other plants,” he tells Newscripts, but those studies focused on making different products than the ones AbbVie wanted. “As medicinal chemists, we care more about the heterocycle-containing molecules because probably at least 50% of pharmaceutical molecules have at least one heterocycle,” Bai says.
Bai and coworkers gave carrots a whirl. Bai chopped up carrots and put them into a reaction flask with water, a bit of ethanol, and a heteroaryl ketone. After 2 days, he had a chiral alcohol. After Bai and coworkers optimized their reaction conditions, they were able to get the chiral alcohols they wanted with up to 99% enantioselectivity. He was surprised that the enzymes, typically persnickety about what they’ll react with, worked with 7 out of 10 of the ketones they tried. Compared with reactions with the orange carrots, those using purple carrots had higher yields overall. This difference may be because the purple ones have more ketone reductants, although the group is unsure, Bai says.
One of the best things about the reaction is how safe it is, Bai says. “Besides the starting ketones, there are literally no toxic reducing chemicals being used. The solvent is just water and trace amounts of ethanol.” It’s also very simple to set up, and the catalyst is pretty inexpensive. Bai got a three-color pack of carrots—orange, white, and purple—from Trader Joe’s for $2.49.
In a previous Newscripts column about chemical-sounding swears, we asked for readers to send in their own chemistry curses. Y’all sure delivered.
“How about ‘stripping’ when purifying your product? Or using ‘butanol’ as a solvent?” Ann Louise Onton asks. “And how about ‘gas chromatography?’ (a form of flatulence?)”
Brett Booker writes that his favorite chemical cuss word is azoles. “I wrote an article on azole alkylation and a British colleague loved saying, ‘We have too many azoles in here, huh Brett!’ ”
And Don Dustin blessed the Newscripts inbox with this anecdote:
“I was amused to see the term ‘Mother Liquor’ on your list of potential chemistry-related swear words in the January 9, 2023 issue of C&EN. Back in the early 1970s, the intramural softball team at the UCLA Chemistry Department was named the Mother Liquors. The Daily Bruin, the campus newspaper, would publish the schedule of intramural games for any given day, and when we saw that the day’s games included the Mother Liquors versus the Master Batters, we were ecstatic. Unfortunately, we found out just how good the Master Batters really were, and we lost 10–1.”
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