My experience:
Last name: Tan
First name: Tee Sin
Drop the Shawn.
In Singapore they will fix it at the CI if there are any problems (for example with the related E-Visa).
We have a more complex problem:
Example: "NEO See Teo Sally MILLER" as in the passport.
I booked already as MILLER Sally or NEO See Teo or NEO Sally. We were never rejected and if the CI staff was not sure they changed the name at the CI-Counter. Seems not uncommon.