I suspect that you are confusing how data are stored with how they are defined and displayed, but anyway:
C = {'L1125';'Y8898';'P41';'5666'}
S = sprintf(',''%s''',C{:});
S = S(2:end)
Note that the leading and trailing single quotes are just an artifact of displaying, they are not actually in the character array (you can easily check this yourself by looking at the character codes).