Nomenclature

I was prepping some dithiothreitol solutions yesterday, and was just wondering about the IUPAC nomenclature. Here's the molecule:

I've seen loads of different names for DTT, common ones include DL-DTT, 1,4-DTT, and 1,4(DL)-DTT. Am I right in saying there are two chiral carbons? (The ones with the hydroxyl group) How do you go about naming it? Apparently the IUPAC systematic name is "(2S,3S)-1,4-Bis-sulfanylbutane-2,3-diol"

Don't need to know for any particular reason, just that I'm very rusty on this sort of chemistry, haven't done it in ages and curiousity got the better of me :smile:

Reply 1

Kaeroll

Ignoring chirality for a moment, the rest of the name should make sense: 1,4-bis-sulfanyl due to the thiol groups at either end, butane- as it's a four-carbon fragment, 2,3-diol for the hydroxyl groups. DTT is simply the trivial abbreviation. (I realise the OP probably knows all this but it's there for any A level students who may be reading and unsure).

The S assignments to each chiral centre are done using the Cahn-Ingold-Prelog priority rules. The highest priority group is that with the highest proton number, and then atomic mass for isomers. In this case, the OH group is of highest priority. Next come two carbon atoms; simply carry on along the chain until a difference is found. So in this case, each chiral centre's second most important group is the alkyl-thiol group next to it, with the SH bound (C-SH vs. C-OH). This leaves the alkyl-hydroxyol group as third and proton as last.

To determine R and S, mentally rotate the molecules so that the hydrogen is pointing away, and trace an arc from priority 1 to priority 3. If the curve goes clockwise, it is R; if it goes anticlockwise, it is S. Molecular models are handy for this. Using this method shows that both centres are (S) configured.

The trivial name appears to use D/L assignments, which arise from the method used by Fischer (I believe) and relate to the chirality of glyceraldehyde. It's commonly used in carbohydrates and amino acids- can't say I've ever seen it used in a thiol, but if it's derived from a carbohydrate or used in biochemistry then I'm not surprised that D/L nomenclature is used.