I suggest you to read relevant information here on link table. Didn't understand how concatenation is causing synthetic key. It would be great if you can share your data model. See some links for your reference
Removing synthetic keys is often easy to accomplish. The easiest solution is to create composite keys by concatenating all key fields into a single new field (please do use a separator character like '-' or '|' between field values) and either renaming or removing the original fields altogether.
That last action may pose a problem, as keys linking multiple fact tables may be easy to create, but many times none of the fact tables contain all key values and their related information. A solution for this could be to concatenate fact tables together, or create a Link Table with all composite key field values, and a few dimension tables that contain the corresponding details.