Process for the preparation of chiral 8-(-3-aminopiperidin-1-yl) xanthines

A process for preparing a compound of the general formula (I)

• or an enantiomer or salt thereof, wherein
• R1 is a phenylcarbonylmethyl, benzyl, naphthylmethyl, pyridinylmethyl, pyrimidinylmethyl, quinolinylmethyl, isoquinolinylmethyl, quinazolinylmethyl, quinoxalinylmethyl, naphthyridinylmethyl or phenanthridinylmethyl group in which the aromatic or heteroaromatic moiety is in each case mono- or disubstituted by Ra, where the substituents may be the same or different and
• Ra is a hydrogen, fluorine, chlorine or bromine atom or a cyano, methyl, trifluoromethyl, ethyl, phenyl, methoxy, difluoromethoxy, trifluoromethoxy or ethoxy group, or
• two Ra radicals that are bonded to adjacent carbon atoms, may also be an —O—CH2—O— or —O—CH2—CH2—O— group,
• R2 is a methyl, ethyl, propyl, isopropyl, cyclopropyl or phenyl group;
• and
• R3 is a 2-buten-1-yl, 3-methyl-2-buten-1-yl, 2-butin-1-yl, 2-fluorobenzyl, 2-chlorobenzyl, 2-bromobenzyl, 2-iodobenzyl, 2-methylbenzyl, 2-(trifluoromethyl)benzyl or 2-cyanobenzyl group,
• the process comprising:
• reacting a compound of the general formula (III) with 3-(phthalimido)piperidine or an enantiomer thereof
• wherein X is a leaving group selected from the group consisting of halogens and sulphonic esters, and R1 to R3 are as defined above to obtain a compound of the general formula (II)
• wherein R1 to R3 are each defined as mentioned above;
• and
• deprotecting the obtained compound of the general formula (II) to obtain the compound of general formula (I).