Well, I dont have a clue what the first one is (4676-39-5 - doesn't show up on chemfinder, are you sure it's the right number?). The second (28281-49-4) is 3,4-methylenedioxypropiophenone (MDP1P).
As for the second part, both 492-39-7 and 14838-15-4 appear to refer to phenylpropanolamine...
Key the numbers into http://www.chemfinder.com (http://www.chemfinder.com)
, you'll see what they are.
Whenever chemfinder can't find what you're looking for, try ChemIDPlus (http://chem.sis.nlm.nih.gov/chemidplus/chemidheavy.jsp)
(http://chem.sis.nlm.nih.gov/chemidplus/chemidheavy.jsp), their database is the most extensive I know of.
--psyloxy--