Right Click

A promising group of apprentice molecular architects….

group

Summer 2015 Research Group. Left to right: Alisa Girard (’16), Josh Sgroi (’16), Julie Laudenschlager (’16) and Kristen Baker (’16).

 

The lab is a hive of activity this summer with two new students, Julie Laudenschlager and Alisa Girard joining Josh Sgroi and Kristen Baker who are returning to continue their research from last summer. They introduced themselves and their research in a blog-post from last July. So let’s meet the new troops and learn something about their research.

Hi! I’m Julie Laudenschlager and I’m a rising senior pursuing a BS in Biochemistry and Molecular Biology. When I’m not in class, I’m also a member of Gettysburg College’s Cross Country and Track teams. I was so excited with the opportunity to work in Dr. Jameson’s lab and to be able to apply the material I learned during my semesters in Organic Chemistry. This was my first semester working through the HHMI program and I enjoyed every minute of it by working alongside Alisa, Kristen and Josh.

Hi! My name is Alisa Girard, and I am a senior Biochemistry and Molecular Biology major with a minor in Studio Art. I spent the summer working in an organic chemistry lab with Julie, Kristen, and Josh under the leadership of Dr. Jameson. Julie and I had similar projects, which focused on attaching ligands to various sugars for biomedical application. This research is particularly interesting to me because I intend to attend medical school after graduation. This experience has given me a background in drug synthesis, which serves as the backbone of clinical trials and treatment.

Summer research was an excellent review of one of the more challenging courses I’ve taken at Gettysburg College: organic chemistry. Core lab techniques, such as column chromatography, extractions and refluxes, were tightened up as they became second nature. In contrast with course lab work, my procedures were not instructional recipes with predetermined outcomes, but instead served as professional means of answering new questions. I also learned some new analytical methods, such as how to perform TLC stains, use the rotovap, and operate the $500,000 NMR machine. It was an absolute honor to have earned a place on the wall of summer chemistry researchers and faculty.

It was especially rewarding to be given my own project, with the security of Dr. Jameson’s guidance. Because Julie and I have similar projects, we could work together to answer common problems and observe how our sugars behaved differently in similar reactions. When Julie and I both found ourselves waiting for a TLC to run, we would play chemistry-themed hangman to keep each other on our toes. It was easy to get into the chemistry groove with the radio playing popular music (as well as some from the 80’s) through the lab. It was relaxing to work on my own assignment at my own pace, rather than race the clock in a classroom setting. It was an absolute pleasure to work toward my own goal, see results, and watch the scientific method take its course in my own hands, or, fume hood.

Summer research in Gettysburg was somewhat of a two-month lifestyle change. Working 9 to 5 during the week kept me productive over summer vacation, without being overwhelming or stressful. My lunch breaks were spent eating large, healthy meals and sharing funny videos with Julie. At least once a week, we’d be surprised with an email that one of the chemistry labs had put out a box of treats for the researchers. It was lots of fun making Miracle Baby cookies with Kristen and Rowan when Dr. Frey took leave from her research and fabulous baking. Outside of the lab, I spent lots of time enjoying a free gym membership, running through the battlefields with Julie, and analyzing The Magic School Bus with my apartment full of physics and chemistry researchers. I also spent some time watching Netflix with friends in Apartment C above us and in what is usually referred to as “Humor House” down the street. This was a fun way of getting to know the other HHMI-supported students on campus.

My free time in the evenings and over the weekend also gave me the opportunity to have dinner with some professors and researchers at the Appalachian Brewing Company and Blue and Grey. This allowed us to wind down a bit, and to discuss our research in a nonacademic setting. Being in Gettysburg over the summer helped me to see the school and town in a new light. I got the chance to experience a quiet, green campus, see the faces of college applicants on tours, and enjoy a few relaxing dinners at local restaurants. I even found the time to go on my first ghost tour! My decision to do summer research was a great one, inside the lab and outside too.

 

Both Julie and Alisa are working on an applying the “click” reaction as a way of appending carbohydrates to synthetic organic molecules. The idea arose while poking around for new bio-organic oriented laboratory experiment, another initiative supported by our HHMI grant. An article in the Journal of Chemical Education described an experiment in which a-D-glucopyranosyl bromide, 2,3,4,6-tetraacetate is converted to b-D-glucopyranosyl azide, 2,3,4,6-tetraacetate, a nice example of an SN2 mechanism, which can be proved by 1H NMR (Fig. 1).

Untitled

Figure 1

 

It turns out that azides are one component of the most important example of the “click” reaction: the Copper-catalyzed Azide-Alkyne Cycloaddition (CuAAC) reaction (Fig. 2a).

Untitled 4

Figure 2

What is a “click” reaction? There is a long list of characteristics, but among the more important are: 1) the reaction must be reliable over a wide range of substrates, 2) must give reliably high yields, 3) must be simple to run and work-up, and 4) must be selective against the wide variety of functional groups found in biomolecules.

The CuAAC reaction is an example of a 3+2 cycloaddition, in this case forming a triazole ring. A cycloaddition is a ring forming reaction and the 3+2 refers to the number of atoms brought together to form the ring: 3 nitrogens from the azide and 2 carbons from the alkyne. The uncatalyzed azide-alkyne cycloaddition (also known as the Huisgen reaction) suffers from the fact that it can give two region-isomers and requires high temperatures (Fig. 2b). Copper catalysis solves both the slow reaction rate and the region-isomer problem.

The glucose azide derivative prepared in the SN2 experiment gives us an ideal reagent for incorporating sugar derivatives into our molecules. The compound is easy to make (Fig. 3) and is general for monosaccharide hexopyranoses and polysaccharides as well. Although we have not incorporated the SN2 reaction into our organic lab curriculum, we have developed an experiment, which demonstrates the utility of the click reaction (Fig. 4).

Untitled 2

Figure 3

 

Untitled 3

Figure 4

 

The route to b-D-glucopyranosyl azide, 2,3,4,6-tetraacetate (Fig. 3) provides some insights into the subtleties of carbohydrate chemistry. Notice that although b-D-glucopyranose has five hydroxyl groups, only one ultimately gets converted to azide. In the first step, the hydroxyl groups are converted to acetates as a way of “protecting” them and to improve the solubility of the carbohydrate in organic solvents. The subsequent steps take place only at a specific position on the pyranose ring: the anomeric carbon. The bromine atom is installed specifically at the anomeric carbon due to the unique stability of the carbocation formed there. We have successfully converted glucose, galactose (both monosaccharides) and cellobiose and maltose (disaccharides) to the corresponding azides. These are all known compounds. Each of these azides have also entered into click reactions and we have successfully prepared our target compounds bearing appended sugars.

How about some pictures from the lab…

image5

A recurring theme of day-to-day life in an organic synthesis lab is the purification of reaction products. One of the most commonly used techniques is column chromatography. In the foreground is a modification of that technique called vacuum column chromatography.

 

 

image1

The result of column chromatography are a series of fractions; basically solutions of the separated compounds as they come off the column (seen lined up along the front of the hood). Although these fractions exhibit a variety of colors, the desired product is white…

 

 

image3

This column looks pretty desperate – the column is black and the collected fraction is black. Believe it or not, a white solid was isolated from this fraction.

 

 

image4

And when all goes well, a nice crystalline product is isolated by vacuum filtration. You can’t see it, but the funnel contains (off)-white crystals and the color remains in the filtrate. The best possible outcome. Unfortunately, it doesn’t always happen that way.

 

Until next summer….

 

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s