Tools such as Toad appeared 2 b very slow.

From mos I quote:

…The bug is fixed in patchset 11.2.0.3 and higher versions.
Release 11.2.0.1 and the patchset 11.2.0.2 are affected by this.

end quote.

Since patching was not an option the workaround has been followed:

Mos note is offering create or replace view ALL_SYNONYMS.. and  to set spfile value (_FIX_CONTROL).

Workaround has been implemented in Test and Preprod environments, no issues found  with it and it showed improvement @  user side.

Happy reading

Mathijs