Alkyl glycosides with long carbohydrate groups are surfactants with attractive properties but they are very difficult to synthesize. Here, a method for extension of the carbohydrate group of commercially available dodecyl-beta-D-maltoside (DDM) is presented. DDM was converted to dodecyl-beta-D-maltooctaoside (DDMO) in a single step by using a CGTase as catalyst and alpha-cyclodextrin (alpha-CD) as glycosyl donor. The coupling reaction is under kinetic control and the maximum yield depends on the selectivity of the enzyme. The Bacillus macerans CGTase favored the coupling reaction,while the Thermoanaerobacter enzyme also catalyzed disproportionation reactions leading to a broader product. range. A high ratio alpha-CD/DDM favored a high yield of DDMO and yields up to 80% were obtained using the B. macerans. enzyme as catalyst. Biotechnol. Bioeng. 2009;104: 854-861. (C) 2009 Wiley Periodicals, Inc.