Indirect and direct approaches in the synthesis of a new mono-6-O-benzyl methylated γ-cyclodextrin as chiral selector for enantioselective gas chromatography

6I-O-Benzyl-2I–VIII, 3I–VIII, 6II–VIII-tricosa-O-methyl-γ-cyclodextrin was synthesized using indirect and direct approaches. The first indirect strategy consists of a multi-step sequence including the ring opening of the permethylated α-cyclodextrin, elongation of the chain with a 6-O-benzyl methylated disaccharide derivative, and macrocyclization. The direct method deals with a selective mono-6-O-TBDMS protection, permethylation, deprotection, and benzylation sequence of γ-cyclodextrin. The results clearly show the higher efficiency of the direct approach but demonstrate the feasibility of the insertion of a modified maltose derivative (indirect method). The new mono-6-O-modified methylated γ-cyclodextrin was used as a selector for the preparation of the new chiral stationary phase. Preliminary enantioselective gas chromatography applications are also reported.

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6I-O-Benzyl-2I–VIII, 3I–VIII, 6II–VIII-tricosa-O-methylcyclomaltooctaoseC78H132O40[α]D = +0.3 (c 1.64, EtOH)Ee = 98%Source of chirality: enantiopure reactant