The concentration of chloramphenicol you are using should be fine, 25ug/ml is pretty typical. You might want to double check though that whomever made the stock solution did it correctly.

I presume the pCC1 plasmid you refer to is the BAC plasmid (there are a few different pCC1 plasmids out there). If so, this is a low copy number plasmid. So you would expect yields to be pretty low. You could check whether your plasmid preparation can transform some fresh cells to chloramphenicol resistance, or you could design a set of PCR primers from some known region of your plasmid and see if you can confirm that way. Lastly you could just try a larger plasmid prep and concentrate the results to see what you get.

Michael J. Benedik thank you for your reply. I am actually purifying the plasmid to remove a construct from it that is in between 2 Sfi1 sites. I cannot get the construct by PCR because it rather long (2000 bp), so we are trying to purify at least 2 ug of plasmid to digest it by Sfi1. It needs to be Sfi1 because I am trying to put the construct into another plasmid through Sfi1 digestion. It's just that my digestion is not working. I don't know if its because of methylation (Sfi1 is sensitive to some methylation) or if it's because I am not even purifying the right plasmid from my cells.

You should be able to PCR a 2kb fragment readily if you use an appropriate polymerase to do so. I have done 5kb and others have done even more. But it sounds like you might just need to work on your purification methods. Low copy number plasmids are challenging sometimes but it certainly is possible to purify microgram quantities.