The invention relates to a derivative of a GLP-1 analogue of a general Formula I, which derivative comprises a side chain attached to a Lys residue at position 34, 35, 36, 37, or 38 of the GLP-1 analogue, which side chain comprises a Branched linker, a 1st and a 2nd Protractor selected from C18 diacid, C20 diacid, and sulfonic acid C16, and at least one Linker element-1 incorporating ethylene glycol units. Linker element-1 may be incorporated in an optional Pre-linker, and/or in a 1st or 2nd Post-linker. The invention also relates to novel GLP-1 analogues, novel side chain intermediate products and their manufacture and use to prepare derivatives of biologically active peptides and proteins, as well as pharmaceutical compositions and medical uses of the analogues and derivatives. The derivatives have very long half-lives while maintaining a satisfactory potency, which makes them potentially suitable for once-monthly administration.