Pergamon I<~cralwdro,~ LEIIPTS, Vol 36. No 45. 8291.8294. 1995 pp. Elsevier Scrence Ltd Printed m Great Britain 0040.4039/95 $9.50+0.00 0040-4039195 )O 1731-x Specific Inhibition of Glycogen Phosphorylase by a Spirodiketopiperazine at the Anomeric position of Glucopyranose Thomas M. Krtille,a Kimberly A. Watsonb Mary Gregorioub Louise N. Johnsonb Sarah Crook,’ David J. Watkin,’ Rhodri C. Griffiths,d Robert J. Nash,d Katerina E. Tsitsanou,” Spyros E. Zographos,’ Nikos G. Oikonomakose and George W. J. Fleeta* aDyson Penins Laboratory, Oxford Centre for Molecular Sciences, South Parks Road, Oxford OX1 3QY UK bLaboratory of Molecular Biophysics, The Rex Richards Building, South Parks Road, Oxford OX1 3QU UK CChemical Crystallography Laboratory, Oxford University, 9, Parks Road, Oxford OX1 UK dInstitute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth, Dyfed SY23 3EB UK eThe National Hellenic Research Foundation, 4X, Vas, Constantinou Avenue, Athens 11635, Greece Abstract: A key intemtediate bicyclic lactone 6 allows control of the anomeric configuration of a spirodiketopiperazine of glucopyranose 5 which is a speciftc inhibitor of glycogen phosphorylase, showing no inhibition of a- and B-glucosidases, a- and P-galnctosidases, P-N-acetylglucosaminidase, pectinase, xylanase or cellulase. Diketopiperazines, both naturally occurring’ and synthetic,’ are a class of bioactive peptides with a range of potential chemotherapeutic applications.’ The preceding paper reports the synthesis of the mannose derivative 1, the first example of a spirodiketopiperazine of a pyranose.4 In a project to discover efficient inhibitors of glycogen phosphorylase (GPb) as possible therapeutic agents for the treatment of diabetes,5*6 a number of derivatives of glucose- 1-carboxylic acids7,8 2 and N-acyl derivatives of P-glucopyranosylamine9 3 have been studied; the best inhibitor in these classes of compounds was the P-N-acetyl derivative 3 (R=Me) with a K1 of 32 PM,“’ a 250.fold improvement over P-D-glucose [K1 7.4 n-M].” The glucopyranose analogue of hydantocidin 4, the first reported spirohydantoin of a pyranose, is a more powerful inhibitor of glycogen phosphorylase with a K1 of 3 PM.” Molecular modelling studies indicated that the spirodiketopiperazine of glucose 5 would bind strongly to GPb and should be a good inhibitor. This paper reports the synthesis of 5 via a bicyclic lactone 6 in which the pyranose ring is already formed and in which the configuration at the anometic centre has been defined: 5 is a highly spectfic - though not as strong an - inhibitor of GPb and has no effect on a number of glycosidases. OH H 5 ZNHCH$ZONti 6 The glucose analogue 5 was prepared from the epimeric azides 7,’ 3 via the key bicyclic intermediate lactone 6 [Scheme l] in which the pyranose ring is already formed and the stereochemistry at the anomeric position has been defined. Hydrogenation of the more readily available glucohepronoazide 7p with palladium black in ethyl acetate gave the amine SD which was coupled by reaction with ZglyOH, dicyclohexylcarbodiimide and 1-hydroxy-benzotriazole in dichloromethane to give 9p in an overall yield of 27%; the low yield in this sequence is due primarily to the aminolactone SD which undergoes relatively easy self condensation to give a compound, the spectral data of which are consistent with the diketopiperazine structure 11. In contrast, hydrogenation of the epimeric azide 7a in the