🚀 go-pugleaf

On Sat, 5 Aug 2006 lucasea@sbcglobal.net wrote:

> <ib.mossin@hotmail.com> wrote in message
> news:1154723407.301122.27420@m73g2000cwd.googlegroups.com...
>
>> Is there any sense in using the d,l system instead of the R,S system 
>> nowadays. The former seems a bit outdated.
>
> To add further confusion, there are also D and L, which are used for 
> sugars (aldoses) as an absolute indicator of stereochemistry, and refer 
> to the configuration of the stereocenter right next to the aldehyde, 
> relative to either D or L glyceraldehyde (if my rusty 25 year old memory 
> serves correctly).  I don't know if, for all sugars, the D isomer (same 
> stereochemistry as D-glyceraldehyde, which rotates polarized light to 
> the right) is the same as the d isomer (the sugar itself rotates 
> plane-polarized light to the right.)

It certainly isn't for amino acids.

> There is yet another use of D and L, for amino acids, but I'm not 
> certain how they're defined--probably relative to alanine, but I'm not 
> sure.

Glyceraldehyde again - swap the CHO for COOH, the OH for NH2, and the 
CH2OH for a sidechain, and you've got an amino acid of the same D/L class.

tom

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