Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watnot!watmath!clyde!rutgers!husc6!wjh12!lotto
From: lotto@wjh12.UUCP
Newsgroups: sci.bio
Subject: Re: Human asymmetry
Message-ID: <66@wjh12.UUCP>
Date: Sun, 12-Apr-87 09:02:03 EST
Article-I.D.: wjh12.66
Posted: Sun Apr 12 09:02:03 1987
Date-Received: Sun, 12-Apr-87 23:37:33 EST
References: <1003@aecom.UUCP> <586@batcomputer.tn.cornell.edu> <3432@udenva.UUCP> <1025@aecom.UUCP>
Reply-To: lotto@wjh12.UUCP (Jerry Lotto)
Distribution: sci
Organization: Harvard Univ. Chem. Dept.
Lines: 44
Keywords: chirality

In article <1025@aecom.UUCP> werner@aecom.UUCP (Craig Werner) writes:
>In article <3432@udenva.UUCP>, agranok@udenva.UUCP (Alexander Granok) writes:
>
>	I see that non-biochemists are troubled by the concept of
>prochirality.  By definition, a prochiral molecule is a symmetric
>(i.e. achiral) molecule that would be made chiral if one of the identical
>atoms (Hydrogen in the above example) were replaced by a third atom,
>Z.  
>	It is true that the identity of the pro-R and pro-S hydrogen
>is absolutely ambiguous unless one knows the priority of the Z group in
>relation to X and Y, but for any given reaction where the products and
>reactants are known, it will be unambiguous.

No.

pro-R / S have a precise definition. It requires that you prioritize
the two identical groups (may be H but also may be anything else) with
respect to each other. The priorities w/ respect to the other (two)
attachments are retained as in the original compound.  It IS true that
biochemical literature has been using stereochemical terminology in a
bastardized fashion for some time, but I cite the original Cahn,
Ingold, and Prelog articles and follow ups by Helmchen and Prelog as
the definitive source of these rules. Chirality is another matter.
See Mislow JACS (1974) for a treatment of symmetry in chemical
structure as it applies to the current nomenclature.

>	Finally, when I said that chemists cannot avoid a mixture of
>enantiomers during a chemical synthesis, while enzymes can be stereochemically
>specific, I did not preclude the possibility of chemists using and/or
>designing enzymes -- but I thought that went without saying.  Obviously,
>to the nitpickers on the net, nothing goes without saying.... 

For crying out loud, since when is tartaric acid an enzyme?  How about
binaps's or any of the hundreds of C2 reagents for hydroboration.
S-valinol? Nor-ephedrine? Chiral phase transfer catalysts?
The list goes ever on. I respect your ability as a biochemist,
but with respect to synthetic organic chemistry, quite a bit of
your commentary SHOULD have gone without saying.


-- 
Gerald Lotto - Harvard Chemistry Dept.
UUCP:  {seismo,harpo,ihnp4,linus,allegra,ut-sally}!harvard!lotto
ARPA:  lotto@harvard.harvard.edu