Glycopeptide phosphonate derivatives

A process for preparing a compound of the formula:

• or a salt thereof;
• wherein
• R20 is —Ra—Y—Rb-(Z)x or —Rf;
• Y is selected from the group consisting of oxygen, sulfur, —S—S—, —NRc—, —S(O)—, —SO2—, —NRcC(O)—, —OSO2—, —OC(O)—, —NRcSO2—, —C(O)NRc—, —C(O)O—, —SO2NRc—, —SO2O—, —P(O)(ORc)O—, —P(O)(ORc)NRc—, —OP(O)(ORc)O—, —OP(O)(ORc)NRc—, —OC(O)O—, —NRcC(O)O—, —NRcC(O)NRc—, —OC(O)NRc—, —C(═O)— and —NRcSO2NRc—;
• each Z is independently selected from hydrogen, aryl, cycloalkyl, cycloalkenyl, heteroaryl and heterocyclic;
• each Ra is independently selected from the group consisting of alkylene, substituted alkylene, alkenylene, substituted alkenylene, alkynylene and substituted alkynylenc;
• each Rb is independently selected from the group consisting of a covalent bond, alkylene, substituted alkylene, alkenylene, substituted allenylene, alkynylene and substituted alkynylene, provided Rb is not a covalent bond when Z is hydrogen;
• each Rc is independently selected from the group consisting of hydrogen, alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, cycloalkyl, substituted cycloalkyl, cycloalkenyl, substituted cycloalkenyl, aryl, heteroaryl, heterocyclic and —C(O)Rd;
• each Rd is independently selected from the group consisting of alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, cycloalkyl, substituted cycloalkyl, cycloalkenyl, substituted cycloalkenyl, aryl, heteroaryl and heterocyclic;
• Rf is selected from the group consisting of alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, cycloalkyl, substituted cycloalkyl, cycloalkenyl, substituted cycloalkenyl, aryl, heteroaryl and heterocyclic;
• and
• x is 1 or 2;
• the process comprising reacting a compound of the formula:
• or a salt thereof, with formaldehyde and H2N—Ra—P(O)(OH)2 under basic conditions.