The invention relates to novel products of formula (I): wherein R 1 represents L-aryl or -L-heteroaryl optionally substituted, such that L represents single bond, alkyl, CO or CO-alk or L'-X with L ' is alkyl and X is O or S; R2 represents H or alkyl; R3 represents alkyl optionally substituted with Hal; R4 represents Hou Hal; these products being in all isomeric forms and salts as medicaments.