[quantum_toothpaste]

As I understand it for each of the animo acids (for example - but it should apply to all chiral molecules I think) there are two chiralities, one is the mirror image of the other -- and if your body synthesized the wrong one you would die.

So my question is how does the process synthesize the correct one? if the atoms are coming together randomly shouldn't it just as likely produce the left handed amino acid rather than the right handed?

[Jorriss]

Yeah, but it's not random. Enzymes mediate certain chiral products over other ones.

[Doc Oc]

I don't know where you heard you'd die, I don't know if that's necessarily the case.  It is true that humans exclusively utilize L-amino acids, which could be part of the reason that enzymes are so incredibly selective in manufacturing one specific enantiomer over another.

In a flask however, you are correct, there is no controlling element and you would end up with a mixture of both enantiomers.  There are many, many, many methods to control stereochemistry in various reactions and lots of books and review articles have covered this topic.

[quantum_toothpaste]

There are many, many, many methods to control stereochemistry in various reactions and lots of books and review articles have covered this topic.

what is a good overview for a beginner?

thanks for all the replies so far too!

[Jorriss]

There are many, many, many methods to control stereochemistry in various reactions and lots of books and review articles have covered this topic.

what is a good overview for a beginner?

thanks for all the replies so far too!

There are asymmetric catalysts that only offer one product, CBS catalyst for example.

There's also metal catalyzed hydrogenation vs metal reduction hydrogenation to control stereochemistry.

You probably already know several ways and you don't realize it

[Biopolmonkey]

I don't know where you heard you'd die, I don't know if that's necessarily the case. 

Do you remember the effect(s) that thalidomide had? Reverse chiralty is hugely detrimental to our bodies, just because we are not designed to cope with those molecules.

[Doc Oc]

I don't know where you heard you'd die, I don't know if that's necessarily the case. 

Do you remember the effect(s) that thalidomide had? Reverse chiralty is hugely detrimental to our bodies, just because we are not designed to cope with those molecules.

Comparing thalidomide to a D-amino acid is comparing apples to oranges.  Re-read my statement, nowhere do I discount the importance of chirality.  The author writes that use of D-amino acids instead of L-amino acids would lead to death.  Because the human body is so exquisitely selective we have no idea what would happen if someone did start making D-amino acids because it doesn't happen.  There are some therapeutic peptides that use D-amino acids for the very reason that they aren't recognized by our body and survive longer than L-amino acid treatments.  But what would happen if one of the enzymes in your body consisted of an oppositely twisted helix?  I don't know, and neither does anybody else.

quantum_toothpaste, I don't know if you have access to online chemistry journals, if you do let me know and I will send you some good review articles.  Here's a few books you can maybe look through:

Principles and Applications of Asymmetric Synthesis.  Lin, G. -Q.  2001
Catalytic Asymmetric Synthesis.  Ojima, I.  2000
Stoichiometric Asymmetric Synthesis.  Rizzacasa, M. A.  2000
Asymmetric Catalysis on Industrial Scale.  Blaser, H. U.  2004

[Biopolmonkey]

@J-bone: Yeah, I see what you're saying and you have a good point. However, as you say, D-amino acids are processed more slowly (if at all ? Been a long time since I was taught this stuff) then if you are only consuming them (in place of L-, and I mean this in terms of nourishment not therapy) it seems to me that there is potential for eg deficiencies. The idea of replacing an enzyme is really interesting ... Wonder if now we have the gene tech. we could aim to do it in something more ethically palatable than a human?


@OP: Apologies for taking the thread off on a slight tangent.