Antigen derivatives and processes for their preparation

A compound of the formula I ##STR10## in which X is a carbonyl group, R.sub.1, R.sub.4 and R.sub.6 independently of one another represent hydrogen tri-lower alkyl-silyl, alkyl having from 1 to 18 carbon atoms, benzyl which is unsubstituted or substituted in the aromatic nucleus by lower alkyl, hydroxyl, lower alkoxy, lower alkylenedioxy, mercapto, lower alkylmercapto, trifluoromethyl and/or halogen, or represent alkanoyl having from 2 to 18 carbon atoms, benzoyl or naphthoyl which are unsubstituted or substituted by halogen, lower alkyl, lower alkoxy, trifluoromethyl, hydroxyl or lower alkanoyloxy, or represent an acyl radical of a lower alkanesulfonic acid or of phenylsulfonic acid, which is unsubstituted or substituted by lower alkyl or halogen, or represent carbamoyl, lower alkyl-carbamoyl or phenyl-carbamoyl, R.sub.2 represents alkyl having 1 to 18 carbon atoms which is unsubstituted or substituted by hydroxy, lower alkoxy, lower alkanoyloxy, halogen, mercapto, lower alkylmercapto, lower alkanoylmercapto, carboxy, lower alkoxycarbonyl and/or carbamoyl, or represents phenyl which is unsubstituted or substituted by lower alkyl, hydroxy, lower alkoxy, lower alkanoyl, lower alkylenedioxy, halogen and/or trifluoromethyl, R.sup.3 represent hydrogen or lower alkyl, at least one of the radicals R.sub.7, R.sub.9 and R.sub.13 represents lower alkyl, and the others represent hydrogen, R.sub.8 is hydrogen, lower alkyl which is unsubstituted or substituted by hydroxy, lower alkoxy, lower alkanoyloxy, mercapto, lower alkylmercapto, lower alkanoylmercapto, amino, lower alkanoylamino, carbamoylamino or cycloalkyl having 5 or 6 carbon atoms, or represents cycloalkyl-lower alkyl having 5 or 6 carbon atoms, in the cyclic moiety, phenyl or phenyl-lower alkyl, in which the phenyl radicals are unsubstituted or substituted as defined above, or heterocyclyl or heterocyclyl-lower alkyl wherein the heterocyclyl radicals are 5- or 6-membered, contain one or two nitrogen atoms in the ring and may or may not contain a fused phenyl radical, R.sub.7 and R.sub.8 together can also represent alkylene having 3 or 4 carbon atoms, R.sub.10, R.sub.11 and R.sub.12 independently of one another represent carboxyl, lower alkoxycarbonyl or carbamoyl which is unsubstituted or mono- or disubstituted at the nitrogen atom by unsubstituted, or carboxy- or carbamoyl-substituted, lower alkyl or by phenyl, benzyl, tetramethylene or pentamethylene or R.sub.11 can also be hydrogen, or a salt of such a compound having a salt-forming group.