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From: lotto@wjh12.UUCP
Newsgroups: sci.bio
Subject: Re: Human asymmetry
Message-ID: <63@wjh12.UUCP>
Date: Wed, 8-Apr-87 15:25:20 EST
Article-I.D.: wjh12.63
Posted: Wed Apr  8 15:25:20 1987
Date-Received: Sat, 11-Apr-87 07:44:37 EST
References: <1003@aecom.UUCP> <586@batcomputer.tn.cornell.edu> <2190@PUCC.PRINCETON.EDU> <1013@aecom.UUCP>
Reply-To: lotto@wjh12.UUCP (Jerry Lotto)
Distribution: sci
Organization: Harvard Univ. Chem. Dept.
Lines: 42

In article <1013@aecom.UUCP> werner@aecom.UUCP (Craig Werner) writes:
><2190@PUCC.PRINCETON.EDU>, 6065833@PUCC.PRINCETON.EDU (Una Smith) writes:
>> In article <1003@aecom.UUCP>, werner@aecom.UUCP (Craig Werner) writes:
>>  
>> >Chemists cannot tell prochiral centers apart, but enzymes can.
>>  
>> Not true; they can deduce their chirality by looking at the structure
>> of derivatives of those molecules.
>
> the pro-R and another in the pro-S,  however, no reaction done by a 
>chemist will differentiate between those two.  Enzymes,however, will,
>pluck one 100% of the time, and the other, none. No mixture of
>enantiomers for enzymes - the same cannot be said of chemists.

Craig,

	Any of the other chemists working on catalytic
enantioselective methodology will be very disappointed to hear this.
The bottom line is that prochiral centers can be modified selectively
only in a chiral environment. Enzymes are certainly some of the most
efficient chemical sources of these environments, but they are not the
only ones.

	The source of chirality may be:
	a) external (environmental) as in a catalyst
	b) local as in a "chiral auxiliary"
	c) internal as in most diastereoselective technology

	Some examples include -
	Reaction		Chiral element			type
	Asymmetric Epoxidation	Di-isopropyl tartrate esters	a
	Modified Aldol		Valinol or Norephedrine imides	b
	OH-directed		Chiral Allylic or Homoallylic	c
		Hydrogenation		Alcohol

	Type a) is the class that enzymes belong in. The ref. for
the example above is J. Am. Chem. Soc. 102, 5974 (1980). There
are a number of other examples as well.
-- 
Gerald Lotto - Harvard Chemistry Dept.
UUCP:  {seismo,harpo,ihnp4,linus,allegra,ut-sally}!harvard!lotto
ARPA:  lotto@harvard.harvard.edu