LDAP With Parameter

Dear Friends,
Here I have 2 stored procedure to return data via LDAP from Active Directory. The first SP it's OK, but the second doesn't.
The difference is in ''@MyDIR'' because in the second I want to use a paramter... How can I use a paramter in the second SP?
THANKS

1.
CREATE PROCEDURE [dbo].[GD_SP_LDAP_CGD_GET_CNsByDIR]
@MyDIR nvarchar(20)
AS

DECLARE @SQLString NVARCHAR(500);
SET @MyDIR ='DSO'

SET @SQLString = N'SELECT * FROM OPENQUERY(ADSI,''
SELECT name
FROM ''''LDAP://OU=DSO,OU=Estacoes,OU=Servicos-Centrais,OU=cgd,DC=GrupoCGD,DC=com''''
'')';

EXECUTE sp_executesql @SQLString;



2.
CREATE PROCEDURE [dbo].[GD_SP_LDAP_CGD_GET_CNsByDIR]
@MyDIR nvarchar(20)
AS

DECLARE @SQLString NVARCHAR(500);
SET @MyDIR ='DSO'

SET @SQLString = N'SELECT * FROM OPENQUERY(ADSI,''
SELECT name
FROM ''''LDAP://OU='' @MyDIR '' ,OU=Estacoes,OU=Servicos-Centrais,OU=cgd,DC=GrupoCGD,DC=com''''
'')';

EXECUTE sp_executesql @SQLString;