Replication Z-field table KNA1 to CRM table BUT000

Hi guys,

I have a requirement to replicate z fields of the ECC table KNA1 in to CRM (table BUT000).  I have been able to successfully replicate the standard fields. However, the custom fields ('z-fields') are not currently being replicated. 

Can anybody help me by identifying the additional configuration and/or development that is needed in order for this to be accomplished? 

Regards,
Ivonne G.