The present invention provides new chemically modified 4-dedimethylaminotetracycline compounds that can be substituted with aryl, alkenyl, or alkynyl groups. The 7, 8, and/or 9 positions and methods for preparing such compounds. Other tetracycline compounds include the 4-dedimethylaminotetracycline derivatives with an oxime group, NH-Alkyl, or N—NH-Alkyl group substituted at the C4 position as well as C2 Mannich derivatives. The present invention also provides a method of treating a mammal suffering from conditions or diseases by administering to the mammal an effective amount of the new chemically modified tetracycline compounds.