Better Living Through Chiral Chemistry

Atario writes "A long time ago, I remember reading in some science magazine that someone had the bright idea of using enantiomers (the two forms of asymmetrical molecules, like left- and right-handed versions of the same one) to make zero-calorie sugar -- turns out, in general, that sugars are all asymmetrical, and everything generates and uses only one of the two chiralities (handednesses) for each one. If we consume a mirrored version of, say, sucrose, we might get all of the sweet but none of the calories. Sweet-tooths rejoice! But nothing ever came of it. Now, however, Wired has an interesting article that explains what the holdup has been and indicates the logjam may break soon, but, as it turns out, in a non-synthetic, albeit nonzero-calorie, way."

Comments

non-nutritive "food"

[dpilot]

Two years of Newtrition investment and research had produced CHOW(TM). CHOW(TM) contained spun, plaited, and woven protein molecules, capped and coded, carefully designed to be ignored by even the most ravenous digestive tract enzymes; no-cal sweeteners; mineral oils replacing vegetable oils; fibrous materials, colorings, and flavorings. The end result was a foodstuff almost indistinguishable from any other except for two things. Firstly, the price, which was slightly hgher, and secondly the nutritional content, which was roughly equivalent to that of a Sony Walkman. It didn't matter how much you ate, you lost weight.*

* And hair. And skin tone. And, if you ate enought of it long enough, vital signs.

From Good Omens, by Terry Pratchett and Neil Gaiman. (pg 110 in my copy)

Stereochemistry - handedness overly simplistic

[Zeio]

Some compounds are listed as d- and l- refer to the highest-numbered asymmetric stereogenic centers. They also do not indicate the sign of rotation of plane-polarized light.

Most interesting organic compounds have multiple stereogenic centers. One of the main reasons plants are used to obtain starting materials for various modern drugs, ergot infested rye (indole substrate), poppies, indica sativa all provide starting points that make it so that creating synthetic materials based on these plant extracts as starting reagents is far easier due to the fact plant enzymes can place each stereogenic center in the right conformation and in wet chemistry this is exceedingly difficult. Mentioning some of the starting plants for illicit drugs is no mistake; they are notoriously sensitive to chiral conformation, and provide some of the most interesting sterochemical research subject matter. Also, due to the draconian laws surrounding federally controlled substances and their precursors, it isn't easy to study these things, despite being hugely important.

To say that stereochemistry is limited to 2-handedness is a ridiculous oversimplification of reality. If I'm not mistaken, C6-H12-O6 "glucose"; has D-glucose has 4 chiral carbon atoms (2^4 = 16 possible stereoisomers) - I believe only one of which is able to provide calories.

Various notations for stereochemistry exist, and one must factor out canonical conformations and take into account the bending of the various stereogenic centers in 3d-space, leading to notations that include "boat" and "chair."

Now, as to the practicality of stereogenics and its use in zero calorie metabolism: this is probably less difficult than separating U238 and U235, but one could probably get an enzyme of modify bacteria to plunk out zero-cal conformations, but in large scale synthetic operations, getting picky with chirality could be problematic / costly. Things are ridiculously hard to separate, and you need to use special techniques such as using tartrate salts and other expensive and slow ways of picking out the various conformations of chiral compounds.