No problem, you can go for this,
V_VALUE = ' ABC DEFG HIJK JKLM NOPQ RST'.
V_SEARCH = 'RST'.
CONCATENATE '\b' V_SEARCH '\b' INTO V_SEARCH.
FIND REGEX V_SEARCH IN V_VALUE.
IF SY-SUBRC = 0.
WRITE 'matched'.
ENDIF.
OR
FIND REGEX '\b' && V_SEARCH && '\b' IN V_VALUE.
Hope this helps.