Method of preparation of a compound of formula: comprising a step a) of glycosylation, preferably in the presence of a Lewis acid, of a compound of formula: with a compound of formula: said step a) providing a compound of formula: wherein: - R 1 represents a linear or branched, saturated or unsaturated C 1 -C 20 alkyl group, optionally substituted; - R 2 represents a linear or branched, saturated or unsaturated C 1 -C 30 alkyl group, optionally substituted; - R 3 represents a C 1 -C 6 alkyl optionally substituted, a C 3 -C 6 cycloalkyl, a C 1 -C 6 acyl or a benzoyl group; and R 4 represents H or C 1 -C 6 alkyl group optionally substituted; or - R 3 and R 4 form together with the nitrogen atom to which they are attached a C 2 -C 6 heterocycloalkyl group or a C 1 -C 5 heteroaryl group; - PG 1 represents a hydroxyl function protecting group; - PG 2 represents a primary amine function protecting group; - PG 3 represents a hydroxyl function protecting group; - PG' 3 represents a hydroxyl function protecting group, optionally forming, together with PG 3 and the oxygen and carbon atoms to which they are connected, a C 3 -C 6 heterocycloalkyl, optionally substituted; and - LG represents a leaving group, and wherein: the term cycloalkyl refers to saturated monocyclic hydrocarbon groups having 3 to 6 carbon atoms, wherein any ring atom capable of substitution may be substituted by a substituent; the term heterocycloalkyl refers to a nonaromatic 5-7 membered monocyclic, ring system having 1-3 heteroatoms and 2-6 carbon atoms, said heteroatoms being selected from O, N, or S, wherein any ring atom capable of substitution may be substituted by a substituent; and the term heteroaryl refers to an aromatic 5-6 membered monocyclic ring system having 1-4 heteroatoms and 1-5 carbon atoms, said heteroatoms selected from O, N, or S wherein any ring atom capable of substitution may be substituted by a substituent. - R 1 represents a linear or branched, saturated or unsaturated C 1 -C 20 alkyl group, optionally substituted; - R 2 represents a linear or branched, saturated or unsaturated C 1 -C 30 alkyl group, optionally substituted; - R 3 represents a C 1 -C 6 alkyl optionally substituted, a C 3 -C 6 cycloalkyl, a C 1 -C 6 acyl or a benzoyl group; and R 4 represents H or C 1 -C 6 alkyl group optionally substituted; or - R 3 and R 4 form together with the nitrogen atom to which they are attached a C 2 -C 6 heterocycloalkyl group or a C 1 -C 5 heteroaryl group; - PG 1 represents a hydroxyl function protecting group; - PG 2 represents a primary amine function protecting group; - PG 3 represents a hydroxyl function protecting group; - PG' 3 represents a hydroxyl function protecting group, optionally forming, together with PG 3 and the oxygen and carbon atoms to which they are connected, a C 3 -C 6 heterocycloalkyl, optionally substituted; and - LG represents a leaving group, and wherein: the term cycloalkyl refers to saturated monocyclic hydrocarbon groups having 3 to 6 carbon atoms, wherein any ring atom capable of substitution may be substituted by a substituent; the term heterocycloalkyl refers to a nonaromatic 5-7 membered monocyclic, ring system having 1-3 heteroatoms and 2-6 carbon atoms, said heteroatoms being selected from O, N, or S, wherein any ring atom capable of substitution may be substituted by a substituent; and the term cycloalkyl refers to saturated monocyclic hydrocarbon groups having 3 to 6 carbon atoms, wherein any ring atom capable of substitution may be substituted by a substituent; the term heterocycloalkyl refers to a nonaromatic 5-7 membered monocyclic, ring system having 1-3 heteroatoms and 2-6 carbon atoms, said heteroatoms being selected from O, N, or S, wherein any ring atom capable of substitution may be substituted by a substituent; and