help with a mod_rewrite statement

Hello,
first a litle explanation
i have a directory stucture of

/home/un/a/
/home/un/a/ann
/home/un/b/bob
/home/un/C/
/home/un/C/Charly

i user mod_rewite so bob is http://www.mydom.com/bob

so to get his working i have (all letters.)
   RewriteCond %{REQUEST_URI} !^[a-zA-Z]/
   RewriteRule   ^/A([^/]+)/?(.*)    /A/A$1/$2  [L]
   RewriteCond %{REQUEST_URI} !^[a-zA-Z]/
   RewriteRule   ^/B([^/]+)/?(.*)    /B/B$1/$2  [L]
   RewriteCond %{REQUEST_URI} !^[a-zA-Z]/
   RewriteRule   ^/C([^/]+)/?(.*)    /C/C$1/$2  [L]
   RewriteCond %{REQUEST_URI} !^[a-zA-Z]/
   RewriteRule   ^/D([^/]+)/?(.*)    /D/D$1/$2  [L]

I am  thinking there must be a beteter way to do it
so i thought i would try
RewriteRule   ^/([a-zA-Z])(.*)  /$1/$1$2 [R,L]


but when i do it, mod_rewrite gets in a nasty loop
in the log file i see
 http://www.mydom.com/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/s/sam

thanks for any help

RP