[curiouscat]

If the final target of my synthesis is known to be bioactive & efficacious  as a racemic mixture  does that mean I can safely ignore optical activity of all the intermediates that will be used for the synthesis? That's what my intuition says. Or not?

In other words, if all I care is to get ultimately a racemic mixture, I won't need to bother if or not any particular intermediate is R or S form?

[discodermolide]

I don't think that is correct.
Unless you specifically do something to the chiral centre it will remain chiral. The (R) or (S) designation may change according to the substituents.
So you will get a diastereoisomeric mixture, especially if you create a second chiral centre some where in the synthesis.

[Zensation]

Building off what discodermolide said.

It also depends on the reactions you are dealing with. Some reactions are naturally racemizing unless there is some sort of catalyst added. Maybe perhaps one step along the reaction the chiral information is lost. Or maybe it isn't.

Depending on your compound, a racemic mixture might have more bioactivity than a pure chiral mixture, sometimes less. Sometimes it is irrelevant. You can't really generalize like this with enantiomers and their biological effects as every compound is different. There are a number of pharmacetucail compounds that are more pronounced with one enantiomer, and some which are more pronounced as a racemic mixture with each enantiomer synergizing the effects of the other.

There also may be cases where the enantiomers behave identically in the body, and if this were the case with your compound, then you could theoretically ignore the chiral centers in your reactions.

You would have to give somewhat specific examples to really get an answer for your question.

[Enthalpy]

AND compounds where one enantiomer has nasty effects!

[curiouscat]

AND compounds where one enantiomer has nasty effects!

Irrelevant in my case (I think).

 Like I said, it is already known that a racemic mixture works. So one enantiomer could at worst be worthless but clearly neither enantiomer is nasty.

[curiouscat]

There are a number of pharmacetucail compounds that are more pronounced with one enantiomer, and some which are more pronounced as a racemic mixture with each enantiomer synergizing the effects of the other.

Interesting. Do you have specific examples for this specific type of effect? Where both enantiomers synergizing the other?  Sounds very elegant.

[curiouscat]

Unless you specifically do something to the chiral centre it will remain chiral. The (R) or (S) designation may change according to the substituents.
So you will get a diastereoisomeric mixture, especially if you create a second chiral centre some where in the synthesis.

You are right. Thanks! After you wrote that now I see why.