SQL & PL/SQL

Hi everybody, i need to do sometingh like this

declare

pdate1 date:=sysdate;
string1 varchar2(1000);

begin

--Sometingh happen here that make lose time...but i need to write in the column the previosly saved sysdate*

string1:='create table a as select b.name, b.surname, b.company, pdate1 as extraction_date from b'

execute immediate string1;

end;

this naturally doesn't work...how i can pass a parameter in the create table made with execute immediate?
Thanks!