Novel compounds

A compound of the general formula I:

• wherein:
• A is a ketone (═O) or A is R5 and R6;
• - - - - represents an optional double bond;
• R1 is a substituted or unsubstituted alkyl group or, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, or (CH2)n—R8;
• R2 is H, substituted or unsubstituted alkyl group or, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group benzyl, or (CH2)p—R9;
• R3 is a protecting group;
• R4 R4 is H, a substituted or unsubstituted alkyl, a substituted or unsubstituted aralalkyl, a substituted or unsubstituted heterocycloalkyl or a side chain group from any one of the naturally or non-naturally occurring amino acids R5 is H or a substituted or unsubstituted alkyl, alkenyl or alkynyl group;
• R6 is a OH or OR7;
• R7 is a substituted or unsubstituted alkyl, a substituted or unsubstituted alkenyl, or a substituted or unsubstituted alkynyl group;
• R8 and R9 are each independently selected from a substituted or unsubstituted aryl, a substituted or unsubstituted aralkyl a substituted or unsubstituted heterocycle or a substituted or unsubstituted heterocycloalkyl;
• and
• n and p are each independently selected from 0-10.