Worpress blog nginx proxy issue

Hi ,

I have a blog on blog.example.com and i am using proxy example.com/blog using nginx. Proxy works fine but i can’t access example.com/blog/wp-admin
it gives a 404 error. I want to change siteurl as well as worpress url to example.com/blog which is the proxy url. When i change siteurl preview of post breaks and when i change the worpress url wp-admin breaks ..Any one can suggest a solution please.

Thanks