You don’t even need to try to extract tokens: CONCEPT_SYNONYM table as well as UMLS source contain concept names in hierarchic form:
Excision of Stomach, Percutaneous Approach for example has synonym “Medical and Surgical @ Gastrointestinal System @ Excision @ Stomach @ Percutaneous @ No Device @ No Qualifier”.
We have previously created early version of transition from ICD10PCS to SNOMED by matching these logical tokens to SNOMED concepts that serve as attributes for procedures concepts.
Here’s more about it: