A process for producing a mutasynthetic sanglifehrin which comprises feeding a sanglifehrin producing bacterium, which is a Streptomyces sp in which the sfaA gene or sfaA gene homologue is inactivated or deleted, a compound of formula wherein X 1, X 2, X 3, X 4, X 5, R 1, R 2, R 3, R 4 and R 5 are defined as R 1, R 2, R 3, R 4 and R 5 independently represent H, F, Cl, Br, C 2-6 -alkenyl or C 1-10- alkyl wherein one or more carbon atoms of said alkyl group are optionally replaced by a heteroatom selected from O, N and S p in which p represents 0, 1 or 2 and wherein one or more carbon atoms of said alkyl group are optionally replaced by carbonyl and which alkyl group may optionally be substituted by one or more halogen atoms; X 1, X 2, X 3, X 4 and X 5 independently represent C or N, and in the case of any of these groups representing N the attached substituent is absent; with the proviso that where R 1, R 3, R 4 and R 5 all represent H and X 1, X 2, X 3, X 4 and X 5 all represent C, then R 2 cannot represent OH; and R 7 represents H or an ester forming group, or a salt thereof, and culturing the bacterium to produce a sanglifehrin compound according to formula or formula below, or a pharmaceutically acceptable salt thereof: wherein: R 1, R 3, R 4 and R 5 independently represent H, F, Cl, Br, C 2-6 alkenyl or C 1-10 alkyl wherein one or more carbon atoms of said alkyl group are optionally replaced by a heteroatom selected from O, N and S p in which p represents 0, 1 or 2 and wherein the alkyl group may optionally be substituted by one or more halogen atoms; and wherein R 2 is selected from H, F, Cl, CF 3, OH, NH 2 and C 1-6 alkyl; X 1, X 2, X 3, X 4 and X 5 independently represent C or N, and in the case of any of these groups representing N the attached substituent is absent; with the proviso that where R 1, R 3, R 4 and R 5 all represent H and X 1, X 2, X 3, X 4 and X 5 all represent C, then R 2 cannot represent OH. wherein X 1, X 2, X 3, X 4, X 5, R 1, R 2, R 3, R 4 and R 5 are defined as R 1, R 2, R 3, R 4 and R 5 independently represent H, F, Cl, Br, C 2-6 -alkenyl or C 1-10- alkyl wherein one or more carbon atoms of said alkyl group are optionally replaced by a heteroatom selected from O, N and S p in which p represents 0, 1 or 2 and wherein one or more carbon atoms of said alkyl group are optionally replaced by carbonyl and which alkyl group may optionally be substituted by one or more halogen atoms; X 1, X 2, X 3, X 4 and X 5 independently represent C or N, and in the case of any of these groups representing N the attached substituent is absent; with the proviso that where R 1, R 3, R 4 and R 5 all represent H and X 1, X 2, X 3, X 4 and X 5 all represent C, then R 2 cannot represent OH; and R 7 represents H or an ester forming group, or a salt thereof, and culturing the bacterium to produce a sanglifehrin compound according to formula or formula below, or a pharmaceutically acceptable salt thereof: wherein: R 1, R 3, R 4 and R 5 independently represent H, F, Cl, Br, C 2-6 alkenyl or C 1-10 alkyl wherein one or more carbon atoms of said alkyl group are optionally replaced by a heteroatom selected from O, N and S p in which p represents 0, 1 or 2 and wherein the alkyl group may optionally be substituted by one or more halogen atoms; and wherein R 2 is selected from H, F, Cl, CF 3, OH, NH 2 and C 1-6 alkyl; X 1, X 2, X 3, X 4 and X 5 independently represent C or N, and in the case of any of these groups representing N the attached substituent is absent; with the proviso that where R 1, R 3, R 4 and R 5 all represent H and X 1, X 2, X 3, X 4 and X 5 all represent C, then R 2 cannot represent OH. R 1, R 3, R 4 and R 5 independently represent H, F, Cl, Br, C 2-6 alkenyl or C 1-10 alkyl wherein one or more carbon atoms of said alkyl group are optionally replaced by a heteroatom selected from O, N and S p in which p represents 0, 1 or 2 and wherein the alkyl group may optionally be substituted by one or more halogen atoms; and wherein R 2 is selected from H, F, Cl, CF 3, OH, NH 2 and C 1-6 alkyl; X 1, X 2, X 3, X 4 and X 5 independently represent C or N, and in the case of any of these groups representing N the attached substituent is absent; with the proviso that where R 1, R 3, R 4 and R 5 all represent H and X 1, X 2, X 3, X 4 and X 5 all represent C, then R 2 cannot represent OH.