In a preferred embodiment, there is provided a protecting group for protecting the thiol side chain of a cysteine residue, the protecting group comprising a Diels-Alder cycloadduct of a furan and a maleimide, and optionally, a linker interposed between the thiol side chain and the Diels-Alder cycloadduct.

The present invention provides a method for preparing S-Bz-MAG3 as a precursor of contrast media. Thioglycolic acid and benzoyl chloride are taken for the thiol protection reaction. Next, N,N′-dicyclohexylcarbodiimide and N-hydroxysuccinimide are converted to corresponding ester compounds. The corresponding ester compounds then react with triglycine by amide bonding reaction. The product of the reaction is recrystallized using acetone, filtered, and finally flushed using flushing agent to give the final product. This is a bifunctional chelator and can be bridged with 99mTc and 186/188Re effectively and applied to nuclear medicine imaging and tumor radiotherapy. By taking advantage of fewer synthesis steps and ease of operations, complicated separation and purification reactions can be reduced and thus achieving highly productivity of S-Bz-MAG3.

In a preferred embodiment, there is provided a protecting group for protecting the thiol side chain of a cysteine residue, the protecting group comprising a Diels-Alder cycloadduct of a furan and a maleimide, and optionally, a linker interposed between the thiol side chain and the Diels-Alder cycloadduct.

In a preferred embodiment, there is provided a protecting group for protecting the thiol side chain of a cysteine residue, the protecting group comprising a Diels-Alder cycloadduct of a furan and a maleimide, and optionally, a linker interposed between the thiol side chain and the Diels-Alder cycloadduct.

Provided herein a method for forming one or more intramolecular disulfide bonds.

In a preferred embodiment, there is provided a protecting group for protecting the thiol side chain of a cysteine residue, the protecting group comprising a Diels-Alder cycloadduct of a furan and a maleimide, and optionally, a linker interposed between the thiol side chain and the Diels-Alder cycloadduct.

Cyclized peptides having a crosslinked structure by one or more intramolecular S—S bonds may be prepared by:

(1-A) as to a completely protected linear peptide having two or more SH groups as functional groups on the peptide, removing protecting groups of all functional groups other than the protected SH groups in the peptide,
(1-B) protecting all SH groups of the linear peptide having two or more SH groups as the functional groups on the peptide by forming a temporary S—S bond,
and
(2) subjecting the peptide obtained by step (1-A) and step (1-B) to a folding step under oxidation and reduction conditions to obtain the cyclized peptide by re-forming an S—S bond in the peptide molecule.

In a preferred embodiment, there is provided a protecting group for protecting the thiol side chain of a cysteine residue, the protecting group comprising a Diels-Alder cycloadduct of a furan and a maleimide, and optionally, a linker interposed between the thiol side chain and the Diels-Alder cycloadduct.

Cyclized peptides having a crosslinked structure by one or more intramolecular SS bonds may be prepared by: (1-A) as to a completely protected linear peptide having two or more SH groups as functional groups on the peptide, removing protecting groups of all functional groups other than the protected SH groups in the peptide, (1-B) protecting all SH groups of the linear peptide having two or more SH groups as the functional groups on the peptide by forming a temporary SS bond, and (2) subjecting the peptide obtained by step (1-A) and step (1-B) to a folding step under oxidation and reduction conditions to obtain the cyclized peptide by re-forming an SS bond in the peptide molecule.

To develop a protecting group that facilitates separation and purification, after reaction, of a compound including a protected functional group, without solidifying or insolubilizing the compound. A xanthene compound of by General Formula (1) ##STR00001## (wherein Y is OR.sup.17 (R.sup.17 is a hydrogen atom or an active ester-protecting group), NHR.sup.18 (R.sup.18 is a hydrogen atom, or a linear or branched C.sub.1-C.sub.6 alkyl group or aralkyl group), an azide, a halogen atom, or a carbonyl group formed together with a methylene group; at least one of R.sup.1 to R.sup.8 is represented by Formula (2);
OR.sup.9X-A(2) and a residue is a hydrogen atom, a halogen atom, a C.sub.1-C.sub.4 alkyl group, or a C.sub.1-C.sub.4 alkoxy group, wherein R.sup.9 is a linear or branched C.sub.1-C.sub.16 alkylene group; X is O or CONR.sup.19 (R.sup.19 is a hydrogen atom or a C.sub.1-C.sub.4 alkyl group); and A is represented by Formula (3) or the like ##STR00002## (wherein R.sup.10, R.sup.11, and R.sup.12, the same or different, are a linear or branched C.sub.1-C.sub.6 alkyl group or an aryl group optionally including a substituent; R.sup.13 is a single bond or a linear or branched C.sub.1-C.sub.3 alkylene group; and R.sup.14, R.sup.15, and R.sup.16 are a linear or branched C.sub.1-C.sub.3 alkylene group)).