Hi @Evgeny_T,
Welcome to the community 
It sounds like you’re working with a Java DTO validation annotation rather than something configured in Tyk. In that context, you typically need to escape twice - once for the string, once for the regex. That means using \\\\ in your string literal to allow a literal backslash.
If this is in relation to Tyk, could you clarify where you’re applying the regex (e.g. in an API definition)? Please share the relevant object so we can better assist.