Compound of the formula X 1 -L-X 2, wherein X 1 is selected from - wherein each R 1 and R 2 is independently from each other selected from H or B, wherein at least R 1 or R 2 is B, wherein - R 3 is selected from H or B, - wherein B is an acid labile amine protecting group, wherein - R 4 is selected from H, C 1 -C 12 -alkyl or aryl, wherein the aldehyde or keto group may be protected by an acid labile protecting group, L is selected from functional linker compounds, that are cleavable nucleophilically from X 2 under basic conditions, in particular L is of the form -T-U-, wherein - T is a spacer between X 1 and U, wherein in particular T is selected from substituted or unsubstituted -C 1 -C 12 -alkyl-, in particular C 1 -C 6 -alkyl, in particular C 1 -C 3 -alkyl, -R 5 -C(=O)-NH-R 6 -, -R 5 -C(=O)-O-R 6 -, -R 5 -C(=O)-O-, -C(=O)-O-R 6 -, -C(=O)-NH-R 6 -, -C(=O), -C(=O)-O-, -R 5 -phenyl-R 6 -, -R 5 -phenyl-, -phenyl-R 6 -, -phenyl-, - wherein R 5 and R 6 are independently from each other selected substituted or unsubstituted C 1 -C 12 -alkyls, in particular C 1 -C 6 alkyls, particularly C 1 -C 3 alkyls, and wherein - U is the cleavage activating part of the functional linker compound, wherein the activating part is formed to stabilize an anion formed during an basic cleavage from X 2, X 2 is of the form -Y-Z, wherein - Y is selected from -O-C(=O)- or -S(=O) 2 -, and - Z is an electron-withdrawing leaving group. X 1 is selected from - wherein each R 1 and R 2 is independently from each other selected from H or B, wherein at least R 1 or R 2 is B, wherein - R 3 is selected from H or B, - wherein B is an acid labile amine protecting group, wherein - R 4 is selected from H, C 1 -C 12 -alkyl or aryl, wherein the aldehyde or keto group may be protected by an acid labile protecting group, - wherein each R 1 and R 2 is independently from each other selected from H or B, wherein at least R 1 or R 2 is B, wherein - R 3 is selected from H or B, - wherein B is an acid labile amine protecting group, wherein - wherein B is an acid labile amine protecting group, wherein - R 4 is selected from H, C 1 -C 12 -alkyl or aryl, wherein the aldehyde or keto group may be protected by an acid labile protecting group, L is selected from functional linker compounds, that are cleavable nucleophilically from X 2 under basic conditions, in particular L is of the form -T-U-, wherein - T is a spacer between X 1 and U, wherein in particular T is selected from substituted or unsubstituted -C 1 -C 12 -alkyl-, in particular C 1 -C 6 -alkyl, in particular C 1 -C 3 -alkyl, -R 5 -C(=O)-NH-R 6 -, -R 5 -C(=O)-O-R 6 -, -R 5 -C(=O)-O-, -C(=O)-O-R 6 -, -C(=O)-NH-R 6 -, -C(=O), -C(=O)-O-, -R 5 -phenyl-R 6 -, -R 5 -phenyl-, -phenyl-R 6 -, -phenyl-, - wherein R 5 and R 6 are independently from each other selected substituted or unsubstituted C 1 -C 12 -alkyls, in particular C 1 -C 6 alkyls, particularly C 1 -C 3 alkyls, and wherein - U is the cleavage activating part of the functional linker compound, wherein the activating part is formed to stabilize an anion formed during an basic cleavage from X 2, - T is a spacer between X 1 and U, wherein in particular T is selected from substituted or unsubstituted -C 1 -C 12 -alkyl-, in particular C 1 -C 6 -alkyl, in particular C 1 -C 3 -alkyl, -R 5 -C(=O)-NH-R 6 -, -R 5 -C(=O)-O-R 6 -, -R 5 -C(=O)-O-, -C(=O)-O-R 6 -, -C(=O)-NH-R 6 -, -C(=O), -C(=O)-O-, -R 5 -phenyl-R 6 -, -R 5 -phenyl-, -phenyl-R 6 -, -phenyl-, - wherein R 5 and R 6 are independently from each other selected substituted or unsubstituted C 1 -C 12 -alkyls, in particular C 1 -C 6 alkyls, particularly C 1 -C 3 alkyls, and wherein - wherein R 5 and R 6 are independently from each other selected substituted or unsubstituted C 1 -C 12 -alkyls, in particular C 1 -C 6 alkyls, particularly C 1 -C 3 alkyls, and wherein - U is the cleavage activating part of the functional linker compound, wherein the activating part is formed to stabilize an anion formed during an basic cleavage from X 2, X 2 is of the form -Y-Z, wherein - Y is selected from -O-C(=O)- or -S(=O) 2 -, and - Z is an electron-withdrawing leaving group. - Y is selected from -O-C(=O)- or -S(=O) 2 -, and - Z is an electron-withdrawing leaving group.