Hi Aamod,
You can call ABAP function module in HANA using HTTP Outbound Connectivity the logic behind it as below.
1 Create Web service or RFC connection in the SAP System and in the service use GUID_CONVERT function module that will return you converted GUID_C22 format.
2.Consume the Web service in HANA using Outbound that will return you expected converted GUID_C22 according to your GUID_16 paramaeter.
3.Use GUID_C22 and search with ITEM table and once get match GUID with table GUID, return the MATNR.
Thanks,
Shambhu Nath