Amides: Humble But Useful
Sep15

Amides: Humble But Useful

A heartfelt thank-you to Chemjobber and See Arr Oh for helpful discussions! CENtral Science’s benevolent overlord, Rachel Pepling, has organized a blog carnival around the theme of "your favorite chemical reaction". For the Haystack's contribution, I thought it would be appropriate to write about a reaction medicinal chemists might find familiar. So I re-read See Arr Oh's post about which types of reactions were really the most common in the med-chem toolkit. I decided on amide formation, which sits just about at the top of the list. I’m not sure it’s my favorite chemical reaction; I’ve got a special place in my heart for the Heck reaction (or Mizoroki-Heck reaction), though I’ve already blogged extensively about it. But every amide bond formation I ran in grad school worked. That’s justification enough for me! Amides are the chemical ties that bind amino acids together to form peptides and proteins. Amides also turn up in a variety of other small molecules that nature makes. So it's not surprising that amides are frequently found in drugs. Take a look at University of Arizona chemist Jón T. Njarðarson's poster of top brand name drugs and marvel at the amide-y goodness. Amide bond formation isn't accomplished by a single, archetypical chemical reaction-- far from it. I thought I'd provide a brief overview of some classic chemistry in this area and then move into a selection of modern-day additions to the amide-construction toolkit. At first glance, it looks like all that’s needed to make an amide is to combine a carboxylic acid and an amine. But to make those two components come together, chemists have had to grease the wheels a bit by activating the carboxylic acid. Converting the carboxylic acid into an acid chloride or acid anhydride are among the oldest of the old-school methods for this. In 1955, MIT chemist John C. Sheehan reported a different idea—use of a coupling reagent, dicyclohexylcarbodiimide (DCC). Classics in Total Synthesis notes that in its time, DCC was "an important advance in the state of the art for forming amide bonds." In fact, Sheehan used it, along with the base potassium hydroxide, in the critical final step of the first total synthesis of penicillin-- construction of the beta-lactam ring of the molecule. However, separation of byproducts from the desired amide can be a limitation of DCC, according to the Haystack's intrepid guest blogger See Arr Oh. Today, "O-chemists have newer, sexier reagents," See Arr Oh adds. Those reagents include N-Ethyl-N′-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDAC), a next-generation version of DCC that's water soluble, and other classes of activating reagents including uronium and phosphonium reagents. John Pokorsi, a student in Karl...

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It’s Chemistry Carnival Time!
Sep07

It’s Chemistry Carnival Time!

A few weekends ago, I was with my young boys at our local mall checking out the kids entertainer, Ryan Buckle & Friends: Science you can sing to. Ryan, the singer, intersperses his songs with science demonstrations. We were there fairly early for a Saturday morning, so his audience was small and consisted mostly of toddlers and preschoolers – not the easiest crowd to entertain. Even though Ryan’s songs were fun to listen and dance to, it was the experiments that captured every one’s attention (yep, parents, too). Smoke vortex rings puffed air as they floated past our heads. Water “disappeared” from a cup thanks to a gel powder. And then came my favorite reaction of all time: The Diet Coke-Mentos geyser. Simple, sure, but way fun to do with kids. As the mints hit the soda, disrupting polar attractions between water molecules, even my two-year old was mesmerized by the foam spewing forth from the bottle. In this International Year of Chemistry, it seems only natural that we should pay tribute to our favorite chemical reactions, be they as simple as a soda geyser or as sophisticated as the Diels-Alder. So, come one, come all, to the greatest chemistry blog carnival this fall! A blog carnival? You betcha. A blog carnival is a periodic collection of blog posts written loosely around a single theme that are then aggregated at the host blog. The beauty of the carnival is that we all can come together around our passion whether we're part of a network or not. Big name bloggers and fledgling writers. Dogs and cats, sleeping together. Everyone is welcome at a blog carnival. But why a blog carnival, you ask? Well, our good friends at the Scientific American blog network, led by The Blogfather Bora Zivkovic, put on a great show with last month's Chemistry Day (blogposts are aggregated here). To acknowledge the World Chemistry Congress taking place in Puerto Rico at the time, Scientific American network bloggers and a few folks invited to the SciAm Guest Blog took to discussing issues of chemistry in their respective disciplines. Bora was even kind enough to invite our own Carmen Drahl (post) and David Kroll (post) to contribute. But the theme there was very general. We've decided to narrow the theme field a bit. If you hadn't gathered by now, the theme of this carnival is...Your favorite chemical reaction. I know, I know. You've identified your reaction and written a brilliant post. But you're thinking, now what the Mizoroki-Heck do I do with it? Send a note to cencarnival@gmail.com with the following information: The title of the post The name...

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Celebrating IYC 2011
Jun28

Celebrating IYC 2011

The International Year of Chemistry is already half over! And what a year it’s been so far. But there’s more to come. This week’s issue of C&EN is our major contribution to the IYC 2011 celebration. The issue contains five essays by prominent figures in the chemistry enterprise on some of the many ways chemistry is contributing to the welfare of humanity, as well as an essay on the life of Marie Curie, who received her Nobel Prize in Chemistry 100 years ago. The issue also contains a Comment by ACS President Nancy B. Jackson that focuses on IYC 2011. Jackson outlines some of the challenges humans face, and writes, “Although no one knows exactly how to address these challenges, we all agree that collaboration and chemistry are crucial in our search for solutions.” For Jackson, “collaboration” means working with chemists from around the world, from developed and developing countries. “Chemical scientists from developing and emerging countries have so much to offer the U.S. chemical community,” Jackson writes. She points, for example, to access to natural products and creative applications of green chemistry. “But most striking,” Jackson writes, “is the personal and professional inspiration that I consistently find through knowing chemists from Africa and other developing regions of the world. Their dedication, enthusiasm, and vision convince me that chemistry really can make the world a better place.” C&EN has been taking note of such chemists during IYC 2011 in a series of profiles of ACS members living and working in places where there are only a few such members. The profiles have appeared in the last issue of each month. So far this year, we have profiled members living in Cuba (where there are a total of six members), Fiji (1 member), Lebanon (13), Burkina Faso (2), and Moldova (1). These stories of chemists working as researchers and educators under difficult conditions and with meager resources are truly inspirational. This week’s issue has a profile of Saida R. Aliyeva, one of eight ACS members living in Azerbaijan. Aliyeva’s research focuses on the microbiology of organisms that degrade crude oil and hydrocarbon products in the Caspian Sea. Her ACS membership, which she began as a postdoc at Washington State University, “opens the door to research collaborations overseas and gives me new opportunities to communicate with many scientists,” Aliyeva told C&EN Senior Editor Mitch Jacoby. ACS has been active throughout IYC. It was one of the sponsors of the IYC kickoff event held at the Chemical Heritage Foundation in Philadelphia in February. Along with Dow Chemical, ACS underwrote a webcast of the event, “Global Challenges/Chemistry Solutions,” which is archived at tinyurl.com/IYCwebcast....

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Seeing IYC 2011 at #acsanaheim
Mar30

Seeing IYC 2011 at #acsanaheim

Signs of the International Year of Chemistry were literally everywhere during this national meeting. They were around the Convention Center … On badges … On jackets … On programs … On shirts … On walls … On floors … On cakes … On bags … On buses … Outside taxi cabs … And even inside of taxi cabs! It’s safe to say that IYC was on everyone’s mind during this national...

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