# Patent

## Title
N and/or Nα derivatized, metal and organic protected L-histidine for coupling to biomolecules for highly efficient labeling with [M(OH2)3 (CO)3]+ by fac coordination

## Abstract

The present invention relates to novel histidine derivates that can be used for the labeling of biomolecules with radioactive metal tricarbonyls. The new derivatives have a histidine that is derivatized at the Nε and at least protected at the Nα and optionally at the Nδ; or derivatized at the Nα and at least protected at the Nα and optionally at the Nδ; or derivatized at the Nε and Nα and at least protected at the Nα and optionally at the Nδ; or derivatized at the Nε; or derivatized at the Nα; or derivatized at the Nε and Nα; or at least protected at the Nα and optionally at the Nδ.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit of PCT/EP04/04683, filed Apr. 29, 2004, which claims the benefit of EP Application No. 2003076252.0 filed Apr. 29, 2003, both of which are incorporated herein in their entirety.
The invention relates to new histidine derivatives that can be coupled to biomolecules, such as amino acids, peptides etc. for labeling with a radioactive metal tricarbonyl [M(OH2)3(CO)3]+ by fac coordination.
The labeling of biologically active molecules with 99mTc for radiopharmaceutical purposes is a field of intense research. The commercially available perfusion agents for radioimaging have to be complemented by labeled vectors which will allow a more precise targeting of various receptors expressed in higher density on i.e. cancer cells. So far, a few compounds are in pre-clinical trials but none has found commercial application so far.
Many chemical and biological difficulties have to be overcome. Chemically, the targeting vector has to be i) derivatized with an appropriate chelator for 99mTc or other radionuclide, ii) should be labeled at high specific activity (low vector concentration) and finally retain its physico-chemical properties and its affinity towards the corresponding receptor. For routine use, the labeling process must be performed preferentially in one single step.
Different procedures are available from literature and for peptides in particular the hynic approach seems to be promising although it suffers from the lack of a clearly defined compound which is required for clinical approval.
The present inventors recently presented the one pot synthesis of the organometallic aqua-ion [99mTc(OH2)3(CO)3]+ (Alberto et al., J. Am. Chem. Soc. 2001, 123, 3135) and showed the versatility of using this complex fragment for the labeling of various biomolecules and peptides in particular.
One of the major advantages of the carbonyl approach is the availability of a well-defined complex with very high specific activity only depending from the ligand type. Naturally occurring bidentate ligands such as N-terminal histidines in peptide chains can efficiently be labeled with [99mTc(OH2)3(CO)3]+. An improvement in respect of specific activity was the introduction of a terminal histidine through the α-amino group which allowed labeling at low ligand concentration.
However, this type of bifunctional chelator has a relatively high lipophilicity and its synthesis is difficult.
It is therefore the object of the invention to provide a differently derivatized histidine which would allow its introduction into or onto any peptide with a minimum of synthetic work and a maximum of labeling efficiency.
The inventors contemplated that since the complex [99mTc(his) (CO)3] is hydrophilic it is appropriate to derivatize the histidine at the ε-nitrogen in the imidazole ring. This functionalization leaves the highly efficient tripodal coordination site untouched but still allows the coupling to amine or carboxylic groups in biomolecules. Finally, since the synthesis of [99mTc(his) (CO)3] can be performed in one single step from [99mTcO4]−, histidine also fulfils the requirement for a one pot labeling procedure without affecting the ligand.
The invention thus relates to histidine derivatives, comprising a histidine that is any one of the following:
a) derivatized at the Nε and at least protected at the Nα and optionally at the Nδ; or
b) derivatized at the Nα and at least protected at the Nα and optionally at the Nδ; or
c) derivatized at the Nε and Nα and at least protected at the Nα and optionally at the Nδ; or
d) derivatized at the Nε; or
e) derivatized at the Nα; or
f) derivatized at the Nε and Nα; or
g) at least protected at the Nα and optionally at the Nδ.
The Nε and/or Nα are derivatized with —(CH2)n—R wherein n=0, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, preferably 1, 2, 3, 4 or 5, and R is a group selected from —NH2, —COOR1, —OH, —X or —X′-biomolecule, wherein X′ is a coupling block having a bond that is the result from a reaction between COOH and NH2, NH2 and COOH, OH and Ph-OH, wherein Ph is phosphoric acid group on the biomolecules, such as phosphorylated peptide or glycosyl phosphates or X and an electrophilic functional group on the biomolecule, in particular S, OH or amine and R1 is H, t-butyl or pentafluorophenyl. X is suitably selected from halides, azides, pseudohalides, phosphate, thiol, silyl.
Either or both of Nε and Nα can be derivatized with a biomolecule. This can be any biomolecule, in particular polypeptides, such as antibodies, peptides, amino acids, sugars, vitamins. Suitable examples of biomolecules are bombesine, (alpha)-MSH peptides, such as melanocortin, octreotate, somatostatin, interleukin-8 (IL8), CCK, (beta)-hairpin loop peptides, neurotensin, biotin, monoclonal antibodies, such as monoclonal antibodies directed against prostate membrane specific antigen (pmsa).
The biomolecule can be coupled directly to the Nε and/or Nα or the Nε and/or Nα can be first derivatized with a group of the formula —(CH2)n—R, wherein R is as defined above.
The Nα and Nδ can be protected with a carbonyl thus forming a six-membered urea ring. Alternatively, Nα, Nδ and the carboxyl group are protected with a metal tricarbonyl.
These two forms of protection are in particular useful when derivatization with —(CH2)n—R is to take place. When subsequently this group is further derivatized with a biomolecule the original protection may be replaced by protection of Nα with a amine protecting group, in particular Fmoc, Cbz, BOC, Teoc, methoxycarbonyl, ethoxycarbonyl, and protection of the carboxyl group by esterification.
After all derivatization steps are completed the histidine derivative can be deprotected and subsequently coordinated to a radioactively labeled metal tricarbonyl to obtain a labeled biomolecule.
The radioactively labeled metal tricarbonyl is suitably selected from [99mTc(OH2)3(CO)3]+, [188Re(OH2)3 (CO)3]+ and [97Ru(OH2)3(CO)3]2+.
According to a further aspect of the invention it was found that coupling of the biomolecule is highly facilitated when the —(CH2)n—R on Nε is derivatized as —(CH2)n—COO-pentafluorophenyl ester. This derivatization leads to an activation of the COOH on Nε, which gives a possibility of direct conjugation with biomolecules without any modification when a biomolecules itself has free carboxylic acid that might be competitive for coupling. In the above situation Nα and the carboxylic part are protected.
The present invention relates in particular to histidine derivatives having one of the following structural formulas










According to a further aspect thereof, the invention relates to biomolecules coupled to a histidine derivative as claimed. The histidine can be at the end or within the biomolecule. Alternatively, both Nε and Nα can be derivatized with a biomolecule leading to dimers or to bifunctional molecules. Examples of bifunctional molecules are molecules in which one side of the biomolecule has a targeting function, such as an antibody or a ligand to a receptor and the other side of biomolecule is used for its toxicity. Other combinations are also part of this invention. Such bifunctional molecules can for example be used for the targeted treatment of tumors. The targeting to a tumor will bring the toxic biomolecule and the radioactive metal in the vicinity of the tumor to be treated.
Suitable biomolecules are bombesine, (alpha)-MSH peptides, such as melanocortin, octreotate, somatostatin, interleukin-8 (IL8), CCK, (beta)-hairpin loop peptides, neurotensin, biotin, monoclonal antibodies, such as monoclonal antibodies directed against prostate membrane specific antigen (pmsa).
In the research that led to the invention two different pathways were found for the introduction of an acetyl group at Nε in Nα, Nδ and —COO protected histidine to afford the model compound Nε—(CH2COOH)-histidine derivative 9. Compounds of the invention, like histidine derivative 9, can be coupled to amino groups in bioactive molecules such as peptides. After full deprotection of such a bioconjugate, histidine provides three coordination sites which efficiently coordinate to [99mTc(OH2)3(CO)3]+ or [Re(OH2)3(CO)3]+ [97Ru(OH2)3(CO)3]2+ in a facial geometry.
The invention thus also provides a method for preparing histidine derivatives of the invention, comprising:
a) providing histidine;
b) protecting at least the Nα and optionally the carboxyl and the Nδ;
c) derivatizing at least one of the Nε and Nα; and
d) deprotecting the protected groups.
The method may further comprise the step e) of labeling the deprotected compound to obtain a labeled compound.
In the method the Nα and Nδ may be protected by a carbonyl group thus forming a six-membered urea ring or the carboxyl, Nα and Nδ may be coordinated to a metal, in particular a metal tricarbonyl.
The derivatization of Nε and/or Nα can be performed with —(CH2)n—R wherein n=0, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, preferably 1, 2, 3, 4 or 5, and R is a group selected from —NH2, —COOR1, —OH, —X or —X′-biomolecule, wherein X′ is a coupling block having a bond that is the result from a reaction between COOH and NH2, NH2 and COOH, OH and Ph-OH, wherein Ph is phosphoric acid group on the biomolecules, such as phosphorylated peptide or glycosyl phosphates or X and an electrophilic functional group on the biomolecule, in particular S, OH or amine, wherein R1 is H, t-butyl. Alternatively, Nε and/or Nα can be directly derivatized with a biomolecule.
When protection is achieved by means of the urea ring and derivatization of —(CH2)n—R takes place at Nå, the ring may be opened prior to introducing the biomolecule. In that case the carboxyl is protected by esterification and the Nα is protected with an amine protecting group, such as Fmoc, Cbz, BOC, Teoc, methyloxycarbonyl, or ethyloxycarbonyl group.
In order to facilitate derivatization, —(CH2)n—R on Nε may first be derivatized as —(CH2)n—COO-pentafluorophenyl ester.
When the method comprises the step of labeling the derivative this is suitably done with a radioactively labeled metal tricarbonyl, in particular a radioactively labeled metal tricarbonyl selected from [99mTc(OH2)3(CO)3]+, [188Re(OH2)3(CO)3]+ and [97Ru(OH2)3(CO)3]2+.
Selective derivatization at the Nε position has thus conveniently been achieved by concomitant protection of Nα and Nδ with a carbonyl group forming a six-membered urea. Cyclic urea ring opening with Fm—OH, coupling of phenyl-alanine as a model to 9 through its primary amine and removal of all protecting groups in one step gave a histidine derivative of phenyl-alanine which could be labeled at 10−5 M with 99mTc in very high yield and even in about 50% yield at 10−6M. The x-ray structure of a complex with [Re(CO)3]+ in which anilin is coupled to 9 confirms the facial arrangement of histidine.
A second pathway applies directly the [Re(CO)3]+ moiety as a protecting group as shown in the scheme below.




This is one of the rare examples in which a metal fragment is used as a protecting group for organic functionalities.

The coordination to histidine protects Nα, Nδ and —COO in one single step, subsequent alkylation with BrCH2COOH(R) at Nε, coupling to phenyl-alanine and oxidative deprotection of [Re(CO)3]+ to [ReO4]− gave the corresponding bioconjugate in which histidine is coupled to phenyl-alanine through an acetylamide at Nε.
Both methods offer convenient pathways to introduce histidine in a biomolecule under retention of its three coordination sites. The procedures are adaptable to any biomolecule with pendant amines and allow the development of novel radiopharmaceuticals or inversed peptides.
Thus, a high yield labeling of biomolecules with [99mTc(OH2)3(CO)3]+ is possible at μM concentrations, when histidine is linked through Nε in the imidazole ring to a targeting molecule. Two convenient strategies to produce such derivatives have been worked out, one employing the [Re(CO)3]+ core as an organometallic protecting group for three functionalities in histidine. The key compounds can be coupled to any amino group in a biomolecule and be labeled in one single step from [99mTcO4]− in water which enables the development of new radiopharmaceuticals.
The derivatization method of choice depends on the biomolecule to be coupled. The opening of the urea ring requires acidic pH and reducing conditions but is generally performed prior to biomolecule coupling. This method is suitable for biomolecules that can withstand such conditions, such as vitamins. Alternatively, polypeptides can be coupled to a histidine that is protected with the metal carbonyl.
Below examples are listed of various types of histidine derivatives for highly efficient and biologically stable labeling of biomolecules.
Nα and Nδ can be protected in one single step, leaving Nε free for further derivatizations. Derivatizations at Nα are possible as well.




The left molecule shows the histidine in which Nα and Nδ are protected and Nε is left for derivatization, which is shown in the right hand molecule. Derivatization (such as alkylation) at Nε leads to a variety of derivatives that can be coupled to biomolecules through the pendant functionality, which can be an amine, a carboxylate, a halide and others. This kind of synthesis is essentially literature known (R. Jain, et al, J. Chem. Soc., Dalton Trans, 1994, 2815). After deprotection, a histidine derivative with possibility of tripodal coordination via the Nα, to [M(CO)3]+ remains:





Before deprotection, molecule 1 can be coupled to a biomolecule of any kind. R can thus also be a biomolecule. Deprotection yields then again a biomolecule that contains a tripodal histidine ligand. This ligand is of highest efficiency in terms of labeling with 99mTc or 188Re and allows the labeling of biomolecules almost on the n.c.a. level.
The following is an example of tripodal histidine coupled to a model peptide sequence:




The combination of synthetic techniques and biomolecule labeling is novel and the high yields unexpected. Moreover, according to the invention the very powerful carbonyl ligand can now be coupled to a biomolecule very easily. Derivatives of the above mentioned type can be coupled to essentially any biomolecule under retention of its physico-chemical properties. Histidine coupled in the way according to the invention is a natural ligand.

Furthermore, histidine derivatives of the invention can be used to reverse the direction of a peptide chain. A normal peptide sequence has for example the following structural formula:




By means of the histidine derivatives of the invention reversed sequences can be produced to yield two N-termini and a bidentate his ligand:




Alternatively a reversed sequence with two C-termini and a bidentate his ligand can be obtained:




Histidine derivatives can also be involved in the peptide chain without reversing the sequence, such as in the following normal sequence with a bidentate histidine ligand in the sequence:




In this case it is possible to include a bidentate, natural ligand in a normal peptide sequence. This inclusion in the peptide chain yields a novel kind of labeling which has not been realized so far.
Modification at Nα in structure yields a semi-natural histidine. Derivatization at either Nα or Nε is selectively possible as follows:




Derivatization at both Nα and Nε is possible at the same time, introducing different functionalities (including also biomolecules) (left) to yield a trifunctional histidine after deprotection, which then gives a trifunctionalized tripodal histidine ligand (right):





Alternatively, coupling of peptide sequences in either R or R1 allows the inclusion of tridentate histidine in a peptide sequence which can be normal (bottom) or reversed (top).





Both strategies allow also the labeling of small molecules by applying the highly efficient and strong histidine ligand. This can be used for i.e. the labeling of amino acids or other small molecules such as hypoxia imaging agents. The [Tc(his-R) (CO)3] complex is thereby of high hydrophilicity which is in general an advantage for biological molecules.
It should be noted that in this application the compounds as depicted in structural formulas I to XVIII are generalized structures. The following Table 1 summarizes the combination of features for each general formula.












TABLE 1







A
B
C
D




















1
II/XIII
IX/X
III/XI
III, XI





XVIII/XI


2
IV/—
np/np
V/XVI
V, XVI


3
VI/—
np/np
VII/XVII
VII, XVII


4
I/XIV
XII/XV
—
histidine





1 = derivatized at Nε


2 = derivatized at Nα


3 = derivatized at Nε and Nα


4 = not derivatized


A = protected by means of six-membered ring


B = protected by means of metal tricarbonyl


C = protected by ester on COOH and amine protecting group on Nα


D = formula with deprotected COOH and Nα from column C for labeling


bold = formula without biomolecule


italic = formula with biomolecule


np = not possible






It is the applicant's intention to disclose herein all possible combinations of the alkyl chain length expressed in the value of n and the various substituents R on Nα and/or Nε. The following is Table 2 in which all possible combinations of n and R are listed. In some of the compounds any one combination of two of the combinations listed below are possible.




















TABLE 2







0
1
2
3
4
5
6
7
8
9
10



























NH2
0/NH2
1/NH2
2/NH2
3/NH2
4/NH2
5/NH2
6/NH2
7/NH2
8/NH2
9/NH2
10/NH2


COOH
0/
1/
2/
3/
4/
5/
6/
7/
8/
9/
10/



COOH
COOH
COOH
COOH
COOH
COOH
COOH
COOH
COOH
COOH
COOH


OH
0/OH
1/OH
2/OH
3/OH
4/OH
5/OH
6/OH
7/OH
8/OH
9/OH
10/OH


X
0/X
1/X
2/X
3/X
4/X
5/X
6/X
7/X
8/X
9/X
10/X









When the biomolecule is not coupled directly to the histidine but when the Nε and/or Nα are derivatized first, the following combinations with n and R are possible.




















TABLE 3







0
1
2
3
4
5
6
7
8
9
10



























NH2
0/NH-
1/NH-
2/NH-
3/NH-
4/NH-
5/NH-
6/NH-
7/NH-
8/NH-
9/NH-
10/NH-



BM
BM
BM
BM
BM
BM
BM
BM
BM
BM
BM


COOH
0/
1/
2/
3/
4/
5/
6/
7/
8/
9/
10/



CO-BM
CO-BM
CO-BM
CO-BM
CO-BM
CO-BM
CO-BM
CO-BM
CO-BM
CO-BM
CO-













BM


OH
0/O-
1/O-
2/O-
3/O-
4/O-
5/O-
6/O-
7/O-
8/O-
9/O-
10/O-



BM
BM
BM
BM
BM
BM
BM
BM
BM
BM
BM


X
0/X′-
1/X′-
2/X′-
3/X′-
4/X′-
5/X′-
6/X′-
7/X′-
8/X′-
9/X′-
10/X′-



BM
BM
BM
BM
BM
BM
BM
BM
BM
BM
BM









NH—BM means that the NH2 on the Nε and/or Nα of the histidine derivative is coupled to the COOH of the biomolecule. In CO—BM the COOH on the Nε and/or Nα of the histidine derivative is coupled to the NH2 of the biomolecule. O—BM means that the OH on the Nε and/or Nα of the histidine derivative is coupled to the Ph-OH or halide on the biomolecules by the formation of a phosphate-ester or an ether linking group of the biomolecule. And X′—BM means that the halide, azide, pseudohalide, phosphate, thiol or silyl on the Nε and/or Nα of the histidine derivative is coupled to S, OH or amine on the biomolecule.

The invention will be further illustrated in the Examples that follows and that is not intended to limit the invention in any way. The Examples describe a model system for the labeling of biomolecules. It should be noted that in the same manner other biomolecules, such as amino acids and peptides can be labeled. In the Example reference is made to the following figures:



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1: Ortep plot of 3, ellipsoids drawn at 50% probability.
FIG. 2: Ortep plot of 6, ellipsoids drawn at 50% probability, showing one of the two molecules in the asymmetric unit.
FIG. 3: Ortep plot of 13, ellipsoids drawn at 50% probability, showing one of the two molecules in the asymmetric unit.



EXAMPLES
Example 1
Synthesis of Nα and Nδ Protected Urea-Histidine (Scheme 1)
5-Oxo-5,6,7,8-tetrahydroimidazo[1,5-c]pyrimidine-7-carboxylic acid methyl ester (molecule 3)
The compound was prepared according to literature with slight modification. (R. Jain et al. Tetrahedron, 1996, 52, 5363) To a solution of L-histidine methylester (2.73 g, 11.28 mmol) in DMF (80 ml) was added Im2CO (1.88 g, 11.61 mmol) at r.t. The reaction mixture was heated to 70° C. for 6 h, cooled down to r.t. and poured slowly to 1M NaHCO3 aqueous solution (250 ml). Some solid precipitated from the water layer, which was extracted with CH2Cl2. During extraction the precipitate dissolved completely in CH2Cl2.
The combined organic extracts were dried over Na2SO4, concentrated under reduced pressure, and purified by flash column chromatography to afford 3 as white solid (1.35 g, 61%). Rf=0.2 (EtOAc 100%); 1H NMR (500 MHz, CD3CN, 25° C.): δ=8.01 (s, 1H; CHim), 6.77 (s, 1H; CHim), 6.61 (br.s, 1H; NH), 4.37-4.34 (m, 1H; CHCO), 3.67 (s, 3H; OCH3), 3.25-3.23 (m, 2H; CH2CH); 13C NMR (500 MHz, CD3CN, 25° C.): δ=172.1, 149.2, 135.4, 126.9, 125.9, 53.6, 53.5, 23.7; MS (ESI): m/z(%): 195.73 (100) [M+], 167.8 (35), 135.8 (24); elemental analysis calcd (%) for C8H9N3O3 (195.18): C, 49.23; H, 4.62; N, 21.54; found: C, 49.32; H, 4.77; N, 21.24.
Crystals suitable for x-ray structure analysis were obtained by slow evaporation from EtOAc.
Example 2
Introduction of Carboxylate Functionality in Nε (Scheme 1)
2-(2-tert-Butoxy-2-oxoethyl)-7-methoxycarbonyl-5-oxo-5,6,7,8-tetrahydroimidazo[1,5-c]pyrimidine-2-ium; bromide (molecule 4)
Bromoacetic acid tert-butyl ester (0.57 ml, 3.86 mmol) was added to a solution of 3 (250 mg, 1.28 mmol) in CH3CN (25 ml). The reaction mixture was refluxed for 24 h, cooled to r.t. and concentrated in vacuo. The residue was washed with Et2O (2×10 ml) and THF (2×5 ml) and dried in vacuo to afford 4 as a white sticky solid, which was used in the next step without any further purification. 1H NMR (300 MHz, D2O, 20° C.): δ=9.39 (s, 1H; CHim), 7.40 (s, 1H; CHim), 5.05 (s, 2H; CH2Nim), 4.78-4.61 (m, 1H; CHCO), 3.63 (s, 3H; OCH3), 3.42-3.39 (m, 2H; CH2CH), 1.39 (s, 9H; tBu); MS (ESI): m/z (%): 309.40 (13) [M+−HBr], 253.80 (100) [M+−HBr—(CH2═C(CH3)2)].
Example 3
Preparation of Nε Protected Histidine (Scheme 1)
Methyl N-[(benzyloxy)carbonyl]-1-(2-tert-butoxy-2-oxoethyl) histidinate (molecule 6)
To a solution of crude 4 (390 mg) in THF (50 ml) were added DIPEA (0.52 ml, 3.01 mmol) and BnOH (2.1 ml, 20.08 mmol). After 16 h of refluxing, the reaction solution was cooled down to room temperature, concentrated under reduced pressure, and purified by flash column chromatography to afford 6 as white solid (260 mg, 62% from 3). Rf=0.15 (CH2Cl2/MeOH 45:1); 1H NMR (500 MHz, CD3CN, 25° C.): δ=7.39-7.32 (m, 6H; 5×CHph, CHim), 6.78 (s, 1H; CHim), 6.66 (br.d, J=7.8 Hz, 1H; NH), 5.06 (s, 2H; CH2—Bn), 4.58 (s, 2H; CH2Nim), 4.42 (q, J=2.6 Hz, 1H; CHCO), 3.62 (s, 3H; OCH3), 2.96 (t, J=5.26 Hz, 2H; CH2CH); 13C NMR (500 MHz, CD3CN, 25° C.): δ=173.2, 168.3, 157.0, 139.1, 138.2, 137.8, 129.5, 129.0, 128.9, 119.2, 83.2, 67.2, 66.9, 55.2, 52.7, 49.3, 30.2, 28.2; MS (ESI): m/z (%): 417.53 (100) [M+]; elemental analysis calculated (%) for C21H27N3O6 (417.48): C, 60.43; H, 6.47; N, 10.07; found: C, 60.43; H, 6.57; N, 9.97.
Crystals suitable for x-ray structure analysis were obtained by vapor diffusion of 1-hexene into EtOAc.
Example 4
Preparation of a Histidine Compound with Deprotected Functionality and Coupling to a Biomolecule (Scheme 2)
Methyl N-[(benzyloxy)carbonyl]-1-{2-[(1-ethoxycarbonyl-2-phenylethyl)amino]-2-oxoethyl} histidinate (molecule 10a)
A solution of 6 (140 mg, 0.34 mmol) in CH2Cl2/TFA (2:2 ml) was stirred for 2.5 h at r.t. The solvent was removed under reduced pressure and dried more in vacuo. The residue, the crude compound 8 was dissolved in CH2Cl2 (10 ml) and neutralized by adding Et3N dropwise. BOP (148 mg, 0.34 mmol) and Et3N (46 μl, 0.34 mmol) were added to the reaction mixture. After 45 min, a solution of phenylalanine-ethyl ester (84.6 mg, 0.37 mmol) and Et3N (51 μl, 0.37 mmol) in CH2Cl2 (10 ml) was added slowly by a syringe. The reaction mixture was stirred for 2.5 d more at room temperature. The solution was diluted with CH2Cl2 (30 ml) and extracted with 1N HCl solution (20 ml), 1N NaHCO3 (20 ml), brine (20 ml). The organic layer was dried over Na2SO4, concentrated under reduced pressure and purified by flash column chromatography to afford 10a as colorless oil (162 mg, 90%). Rf=0.2 (CH2Cl2/MeOH 40:1); 1H NMR (500 MHz, CD3CN, 25° C.): δ=7.37-7.28 (m, 9H; 2×4H—CHph, CHim), 7.16 (d, J=8.23 Hz, 2H; 2×CHph), 6.77 (br.d, J=7.65 Hz, 1H; NH), 6.69-6.66 (m, 2H; CHim, NH), 5.05 (s, 2H; CH2—Bn), 4.61 (dt, J=7.86 Hz, 1H; CH-Phe), 4.52 (s, 2H; CH2Nim), 4.43-4.41 (m, 1H; CHCO), 4.11 (q, J=7.15 Hz, 2H; CH2CH3), 3.62 (s, 3H; OCH3), 3.10 (dd, J=8.19 Hz, 1H; CH2-Phe), 2.99-2.93 (m, 3H; CH2-Phe, CH2CH), 2.57 (s, N—CH3), 1.18 (t, J=7.13 Hz, 3H; CH3); 13C NMR (500 MHz, CD3CN, 25° C.): δ=173.3, 172.0, 167.8, 157.0, 139.1, 138.3, 138.2, 137.8, 130.4, 129.5, 129.4, 129.0, 128.9, 127.9, 118.9, 67.2, 62.2, 55.2, 54.8, 52.8, 49.9, 38.0, 30.3, 14.5; MS (ESI): m/z (%): 537.53 (100) [M++H]; elemental analysis calcd (%) for C28H32N4O7+0.5[N(CH3)2]3P═O+0.5H2O (634.5): C, 58.63; H, 6.62; N, 12.14; found: C, 58.98; H, 6.89; N, 12.48.








Example 5
Introduction of a Functional Group at Nε in [Re(CO)3]+ Protected Histidine (Scheme 3)
Re Complex (16a)
To a solution of complex 14, (25 mg, 0.059 mmol) and CS2CO3 (20.4 mg, 0.065 mmol) in acetonitrile (25 ml) ethyl bromoacetate (29.5 mg, 0.176 mmol) in acetonitrile (5 ml) was added. The reaction mixture was heated at 35° C. for 1.5 h. Glacial acidic acid was added to the mixture to neutralize. After standard work-up, the crude substance was purified by a silica gel chromatography to provide complex 16a (30 mg, 90%). Rf=0.15 (EtOAc/EtOH 5:1); 1H NMR (300 MHz, CD3CN, 20° C.): δ=7.95 (s, 1H; CHim), 6.92 (s, 1H; CHim), 4.78 (s, 2H; CH2Nim), 4.23-4.16 (q, J=7.1 Hz, 2H; CH2CH3), 3.91-3.87 (m, 1H; CHCO), 3.21-2.98 (q, 2H; CH2CH), 1.28-1.23 (t, J=7.5 Hz, 3H; CH3); 13C NMR (300 MHz, CD3CN, 20° C.): δ=199.5, 197.8, 197.8, 181.8, 168.8, 143.4, 135.7, 120.9, 63.0, 52.6, 49.4, 28.7, 14.4; MS (ESI): m/z (%): 511.8 (100) [M++H], 1020.7 (55) [2M+]; elemental analysis calcd (%) for C15H18N3O7Re (510.5): C, 30.59; H, 2.76; N, 8.23; found: C, 30.84; H, 3.0; N, 8.06.
Re Complex (16b)
The preparation is similar to compound 16a. To compound 14, (25 mg, 0.059 mmol) and Cs2CO3 (20.4 mg, 0.065 mmol) in acetonitrile (25 ml) was added tert-butyl bromoacetate (34.5 mg, 0.176 mmol). The reaction mixture was stirred at 35° C. for 1.5 h. The reaction mixture was filtered, dried under vacuum and purified by silica gel chromatography (EtOAc/EtOH 5:1) to yield complex 16b (29 mg, 90%). 1H NMR (300 MHz, CD3CN, 20° C.) δ=7.93 (s, 1H; CHim), 6.90 (s, CHim), 4.65 (s, 2H; CH2Nim), 3.94-3.25 (m, 1H; CHCO), 3.27-3.23 (q, 2H; CH2CH), 1.45 (s, 9H; tBu); 13C NMR (CD3CN) □δ=181.3, 167.3, 143.1, 135.2, 120.6, 83.8, 52.3, 49.7, 28.5, 28.0, 27.8; MS (ESI): m/z (%): 539.9 (100) [M+], 1076.8 (50); elemental analysis calcd (%) for C15H18N3O7Re (538.5): C, 33.43; H, 3.34; N, 7.80; found: C, 33.30; H, 3.85; N, 7.68.
Re Complex 15
To hydrolyze the ester groups, compound 16a (30 mg, 0.057 mmol) was stirred in a solution of methanol (5 mL) and LiOH (0.5 M, 2 ml) overnight at room temperature and compound 16b (15 mg, 0.028 mmol) was stirred in a solution of methylene chloride (2 ml) and trifluoroacetic acid (2 ml) for 2 hours at room temperature. Two crude substances were purified by column chromatography (EtOH/THF/AcOH 10:1:0.1) to yield complex 15 (95% and 90% respectively).
Example 6
Coupling of a Biomolecule to the Carboxylate Group in [Re(CO)3]+ Protected Histidine and Removal of the [Re(CO)3]+ Protecting Group (Scheme 4)
Re Complex 17
To the solution of the complex 15 (8 mg, 0.02 mmol) in a mixed solution of CH2Cl2/DMF (3:0.2 ml) were added BOP (7.4 mg, 0.02 mmol) and Et3N (2 μl, 0.02 mmol) at room temperature. After 30 min, a solution of phenylalanine-ethyl ester (4 mg, 0.02 mmol) and Et3N (2 μl, 0.02 mnol) in CH2Cl2 (2 ml) was added dropwise to the complex solution by syringe. The reaction mixture was stirred overnight. The reaction solution was concentrated in vacuo. The residue was treated with diethyl ether (2×5 ml). The white solid was dissolved in THF (10 ml) and insoluble solid was filtered off. The filtrate was concentrated in vacuo to provide the ethyl ester of complex 17 (75%). 1H NMR (500 MHz, CD3CN, 25° C.): δ=7.8 (s, 1H; CHim), 7.34-7.21 (m, 5H; CHph), 6.8 (s, 1H; CHim), 4.63-4.59 (m, 1H; CHCO), 4.53 (d, 2H; CH2Nim), 4.08 (q, 2H; CH2CH3), 3.92-3.88 (m, 1H; CH-His), 3.18-3.10 (2×dd, 2H; CH2-His, CH2-Phe), 3.05-2.96 (2×dd, 2H; CH2-His, CH2-Phe), 1.17 (t, 3H; CH3); 13C NMR (500 MHz, CD3CN, 25° C.): δ=198.1, 196.6, 196.5, 180.4, 170.8, 165.5, 142.0, 136.7, 134.3, 129.4, 128.4, 126.8, 124.9, 120.3, 119.6, 61.2, 54.1, 51.4, 49.2, 37.2, 27.7, 13.4; IR (KBr): ν=2020, 1886, 1733, 1636 cm−1; MS (ESI): m/z (%): 659 (100) [M++H]; elemental analysis calcd (%) for C22H24N4O8Re (658.6): C, 40.12; H, 3.67; N, 8.51; found: C, 39.31; H, 3.83; N, 8.25.
Ethyl ester group of the complex was hydrolyzed by stirring the complex in mixed solution of 0.5M LiOH and MeOH (1:2) for overnight at room temperature, as mentioned above, to afford complex 17 quantitatively.
General Procedure for the Oxidation of Rhenium from Complex 17 and 15
A solution of compound 17 or 15 (5 mM in H2O, 500 μl) and acid (HCl, TFA, or acetic) solution (1.0, 0.1, or 0.01M in H2O, 70 μl) were added to a vial, which was sealed then degassed with nitrogen (10 min). H2O2 (0.43, 0.86, or 1.29M in H2O, 60 μl) was added to the degassed vial, followed by heating the sample at 50° C. Monitoring of the reaction mixture was conducted by HPLC at 250 nm, where the reaction mixture (10 μL) was injected on the HPLC at 4, 8, 24, and 48 hrs or until the rhenium complex was not visible in the spectrum. The effectiveness of the reaction condition was calculated by determining the peak area ratio of the rhenium complex over the formation of perrhenate. When the rhenium complex was no longer observed, the reaction mixture was treated with manganese dioxide to remove residual H2O2 from the reaction mixture then filtered with a Wattman 0.2 μm filter to yield the uncoordinated ligand in solution to be used in 99mTc labeling.








Example 7
Preparation of Histidine with an Nε pendant —NH2 group (Scheme 5)
3-(1-[3-(9H-Fluoren-9-ylmethoxycarbonylamino)-propyl]-1H-imidazol-4-yl)-2-(3-trimethylsilanyl-propionylamino)-propionic acid methyl ester (molecule 18)
A mixture of 3 (196 mg; 1.0 mmol) and N-Fmoc-3-iodopropylamine (1.22 g; 3.0 mmol) in MeCN (40 ml) was heated at reflux for 4.5 days. When compound 3, urea derivative, was not detectable by TLC, the reaction mixture was concentrated in vacuo, resulting in a white solid. The solid material was redissolved in MeCN (40 ml) and 2-trimethylsilylethanol (355 mg; 3.0 mmol) and dipea (259 mg; 2.0 mmol) were added. The resulting mixture was stirred at RT under N2 for 16 hrs. The solvent was removed in vacuo, followed by purification by column chromatography (silica; EtOAc). Yield: 316 mg (53% over two steps) of a foamy colourless solid Found: C, 62.1; H, 6.2; N, 9.5; Calc. for C31H40N4O6Si: C, 62.8; H, 6.8; N, 9.5; νmax (KBr)/cm−1 3329br NH, 1730s, 1698vs C═O; δH (300.8 MHz; CD3CN) 7.82 (2H, pseudo-d, 2×ArH), 7.64 (2H, pseudo-d, 2×ArH), 7.38 (3H, m, 2×ArH+N2CHHis), 7.32 (2H, pseudo-t, 2×ArH), 6.79 (1H, s, CHHis), 6.55 (1H, d, J 7.5, NH), 5.68 (1H, br s, NH), 4.35 (3H, overlapping m, OCH2−Fmoc+CαH), 4.22 (1H, t, J 6.6, OCH2CH−Fmoc), 4.07 (2H, m, CH2), 3.87 (2H, m, CH2), 3.60 (3H, s, OCH3), 2.99 (2H, m, CH2), 2.90 (2H, m, CβH2), 1.85 (2H, m, CH2), 0.93 (2H, m, CH2), 0.01 (s, 9H, Si—(CH3)3). δC (CD3CN; 75.47 MHz) 173.7 (C═Oester), 157.7, 157.6 (2×C═Oamide), 145.5, 142.2 (2×ArCq), 138.4 (CHis), 128.9, 128.3 (2×ArCH), 126.4 (CHis), 121.2, 118.6 (2×ArCH), 118.1 (CHis), 66.9, 63.7, 55.3, 52.7, 48.3, 44.9, 38.6, 32.1, 30.1, 18.3, 1.4 (Si(CH3)3); m/z (ESI-pos., MeOH) 343, 371, 533, 593 [M+H]+.
3-[1-(3-amino-propyl)-1H-imidazol-4-yl]-2-(3-trimethyl silanyl-propionylamino)-propionic acid methyl ester (molecule 19)
Compound 18 (255 mg; 0.43 mmol) was dissolved in a 1/1 DMF/NEt2 mixture (8 ml). After the mixture was stirred for 1 hr at RT, the solvent was removed in vacuo. Purification by preparative HPLC (C-18ec column; TFA buffer) afforded compound 19 as a colourless foamy solid as its trifluoroacetate salt. Yield: 190 mg (91%).
δH (300.08 MHz; CD3CN) 8.59 (1H, s, N2CHHis), 7.95 (3H, br, NH3+), 7.26 (1H, s, CHHis), 6.56 (1H, d, J 8.4 Hz, NH), 4.43 (1H, m, CαH), 4.24 (2H, t, J 6.9 Hz, CH2), 4.05 (2H, m, CH2), 3.68 (3H, s, OCH3), 3.22 (1H, m, CβH), 3.06 (1H, m, CβH), 2.95 (2H, t, J 6.9, CH2), 2.21 (2H, m, CH2), 0.89 (2H, m, CH2), 0.00 (9H, s, Si—(CH3)3); δC (75.47 MHz; CD3CN): 172.7 (C═Oester), 162.2 (q, Jc, F 34.6, CF3), 157.7 (C═Oamide), 135.9, 132.4, 120.7 (3×CHis), 64.0, 54.6, 53.2, 47.0, 37.3, 28.6, 27.6, 18.2 (OCH3, Cα, Cβ+5×CH2), 1.5 (Si—(CH3)3); m/z (ESI-pos.; MeOH): 343.1, 370.8 ([M+H]+, C16H30N4O4Si requires 371.2) 762 [2M+Na]+.
Example 8
Coupling of Biomolecules to Amino Group in Histidine Derivative (Scheme 5)
a) biotin: D-(+)-Biotin (35 mg; 0.14 mmol) was dissolved in a 4/1 (v/v) mixture of DMF/NEt3 (2.5 ml). To this mixture was added a solution of compound 19 (91 mg; 0.19 mmol) in DMF (2 ml), followed by addition of TBTU (46 mg; 0.14 mmol). After the mixture was stirred for 45 min at RT, it was evaporated to dryness in vacuo. The residue was taken up in 2M NaHCO3 (20 ml) and extracted with CH2Cl2 (3×20 ml). The combined organic layers were washed with 0.5 M HCl (20 ml), H2O (20 ml) and brine (2×20 ml). After removal of the solvent, compound 20 was obtained as a colourless foamy solid. Yield: 67 mg (78%; relative to biotin).
δH (300.08 MHz; CD3OD) 7.60 (1H, s, N2CHHis), 6.95 (1H, s, CHHis), 4.48 (1H, m), 4.41 (1H, m), 4.29 (1H, m), 4.09 (2H, m), 3.98 (2H, m), 3.69 (3H, s, OCH3), 3.16 (3H, overlapping-m, CH2+H), 2.95-2.78 (5H, overlapping-m, 2×CH2+H), 2.70 (1H, m), 2.19 (2H, m, CH2), 1.93 (2H, m, CH2), 1.63 (4H, m, 2×CH2), 1.43 (2H, m, CH2), 0.94 (2H, m, CH2), 0.01 (9H, s, Si—(CH3)3; δC (75.47 MHz; CD3OD): 176.4, 174.3 (C═Oester+N2C═O), 166.3, 158.9 (C═Oamide), 138.5, 138.3, 118.7 (ArCHis), 64.2, 64.4, 61.7, 57.1, 55.7, 52.8, 45.7, 41.1, 37.4, 36.8, 31.9, 31.1, 29.8, 29.5, 26.8, 18.6 (10×CH2, Cα, Cβ, OCH3, 3×CH), 1.5 (Si—(CH3)3; m/z (FAB+; NBA) 597.2898 (M+, C26H45N6O6SiS requires 597.2891).
b) to enkephalin: To a solution of purified compound 19 (39 mg; 0.08 mmol) and protected enkephalin (85 mg; 0.08 mmol) in DMF (1.5 ml) and NEt3 (0.5 ml) was added TBTU (25 mg; 0.08 mmol). The mixture was stirred for 45 mins at RT and concentrated to dryness in vacuo. The compound was purified by HPLC (run 1: C8-column; 50 mM TRIS buffer; run 2: C8-column; TFA buffer). Yield: 42 mg (49%) of compound 21 as glassy solid.
δH (500.25 MHz; CD3OD) 8.77 (1H, s, N2CHHis), 7.43 (1H, s, CHHis), 7.28 (4H, m, 4×ArH), 7.20 (1H, m, ArH), 7.12 (2H, pseudo-d, 2×ArH), 6.90 (2H, pseudo-d, 2×ArH), 4.52 (1H, m, CαH), 4.49 (1H, m, CαH), 4.22-4.09 (7H, overlapping m, 2×CαH+2×CH2), 3.85 (2H, m, CH2-Gly), 3.78 (2H, m, CH2-Gly), 3.73 (3H, s, OCH3), 3.25-3.02 (9H, overlapping m, 2×CH2+3×CβH), 2.84 (1H, m, CβH), 2.04 (1H, m, CH2—CH2—CH2), 1.71 (1H, m, CγH-Leu), 1.56 (2H, m, CβH2), 1.36 (9H, S, OC(CH3)3), 1.28 (9H, S, OC(CH3)3), 0.94 (3H, d, J 6.3, Leu-CH3), 0.89 (3H, d, J 6.3, Leu-CH3); δc (90.5 MHz; CD3OD) 175.5, 175.1, 174.2 172.9, 172.6, 158.7, 158.2 (C═O,), 155.4, 138.3, 136.4, 133.6, 130.9, 130.2, 129.6, 128.0, 125.2, 121.2 (all ArC), 81.0, 79.6 (Cq), 64.5, 58.0, 57.5, 54.4, 53.2, 47.6, 44.1, 41.0, 38.1, 38.0, 36.3, 30.8, 29.2, 28.7, 28.2, 25.9, 23.5, 21.7, 18.6, −1.5 (CH, CH2 and CH3;); m/z (FAB+; NBA) 1064.5789 ([M+H]+, C53H82N9O12Si requires 1064.5852)




Example 9
Coupling of Two Functional Groups to Nε and Nα (Scheme 6)
2,6-Bis-tert-butoxycarbonylmethyl-7-methoxycarbonyl-5-oxo-5,6,7,8-tetrahydro-imidazo[1,5-c]pyrimidin-2-ium; bromide (molecule 22)
NaH 13 mg (0.307 mmol) was suspended in dried DMF (2 ml) at 0° C. A solution of compound 3 60 mg (0.307 mmol) in DMF (1 ml) was added slowly dropwise. The reaction mixture was stirred at 0° C. for 30 min and at room temperature for 1 h more until no gas was evolved. The reaction solution was cooled down to 0° C. again. Bromoacetic acid tert-butyl ester 0.07 ml (0.461 mmol) was added by syringe very slowly at cold condition. The solution was stirred at 0° C. for 30 min and at r.t. for 2 hrs more. When the compound 3 was not detectable by TLC, bromoacetic acid tert-butyl ester 0.14 ml (0.921 mmol) was added once more dropwise. The reaction mixture was heated to 70° C. for overnight. The reaction was monitored by TLC. After 15 hours of heating, the solution was cooled down to r.t. and concentrated in vacuo. The crude reside was treated with diethyl ether twice to remove excess of bromide and dried in vacuo. The crude compound 22 was used for next step without further purification. MS (ESI): m/z: 424.56 [M−Br]+
2-[tert-Butoxycarbonylmethyl-(9H-fluoren-9-yl-methoxy carbonyl)-amino]-3-(1-tert-butoxycarbonylmethyl-1H-imidazol-4-yl)-propionic acid methyl ester (molecule 23)
The crude compound 22 was dissolved in acetonitrile (10 ml) at r.t. Fm—OH 181 mg (0.921 mmol) and DIPEA 0.08 ml (0.461 mmol) were added. After 24 hours of stirring at r.t., the reaction solution was neutralized by adding 1N HCl solution and concentrated under reduced pressure. The residue was dissolved in CH2Cl2 and extracted with water once and 1N HCl solution once. The organic layer was dried over Na2SO4, concentrated in vacuo and purified by flash column chromatography afforded compound 23 (yield: 40-50% from compound 3).




Example 10
Preparation of Activated Histidine Derivative
2-(9H-Fluoren-9-ylmethoxycarbonylamino)-3-(1-pentafluoro phenyloxycarbonylmethyl-1H-imidazol-4-yl)propionic acid methyl ester (molecule 24): Compound 9 (0.198 mmol) was dissolved in THF (3 ml) and pyridine was added to neutralize the solution pH 6-7. Pyridine 0.03 ml (0.396 mmol) was added. Then after a solution of trifluoroacetic acid pentafluoro-phenyl ester (TFA-Pfp) 111 mg (0.396 mmol) in THF (2 ml) was added dropwise by syringe very slowly at r.t. After 19 hours of stirring the reaction mixture at r.t., the solution was concentrated in vacuo. The crude residue was dissolved in dichloromethane and extracted with 0.5N HCl once, 0.5N Na2CO3 once and brine once. The organic layer was dried over Na2SO4, concentrated in vacuo, and purified by flash column chromatography afforded compound 24. (Yield: 55%); MS (ESI): m/z: 615.78 [M+H]+




Example 11
General Coupling Procedure of Histidine Derivative to Peptide
Coupling: Compound 9 or 24 was used for the coupling reactions. One of the ligands (normally 0.02-0.08 mmol) was dissolved in DMF and Et3N or DIPEA (0.03-0.1 mmol) was added as a base. In case of compound 9, BOP or TBTU (normally 0.025-0.09 mmol) was added as a coupling reagent, so that the carboxyl acid group of the ligand was activated in 30 min at room temperature. Then after, a solution of a peptide (normally 0.01-0.02 mmol) in DMF, such as (beta)-hairpin loop peptide, RGD, or bombesin was added dropwise by syringe. In case of compound 24, without coupling reagent, a peptide solution was added right after addition of base. The compound 24 is more suitable when the peptide has a free carboxylic acid group, such as Phe-Gly-OH, Gly-Pro-OH, Gastrin (7 free COOH in structure), or TOCA-OH. Depending on the peptide, the reaction mixture was stirred 2-18 hours. The reaction was monitored by HPLC. When the peptide was not detectable by HPLC, the reaction solution was concentrated in vacuo. The crude residue was purified by preparative HPLC and the product was conformed by MS.
Deprotection: A histidine conjugated peptide (normally 0.003-0.006 mmol) was dissolved in piperidine (1 ml) at room temperature. After 30-40 min of stirring, the reaction mixture was poured into ice-cold water (3 ml). The white solid, fulvine, was filtered and rinsed with water (1 ml). The aqueous solution was concentrated in vacuo to provide white solid as an all, Fmoc and methyl ester, deprotected product that was used for labeling without further purification.
Labeling: A solution of a conjugate (10−3 or 10−4 M in water or phosphate buffer (pH7.4), 100 μl) was added to a vial. Then a solution of [99mTc(CO)3(H2O)3]+ (900 μl) was added to the vial (total concentration: 10−4 or 10−5 M). The solution was heated 90° C. for 30 min to 1 hour. Normally the labeling was done quantitatively in 30 min in concentration of 10−4 M and 20 to 50% in 30 min in concentration of 10−5 M. In case of (beta)-hairpin loop peptide, its conjugate showed quantitative labeling in 30 min even in concentration of 10−5 M.
Example 12
General Labeling Procedures
A solution of ligand (10−3 or 10−4 M in H2O, 100 μl) obtained from either organic synthesis or through rhenium oxidation pathway was added to a vial, which was then sealed and degassed with a stream of nitrogen gas for 10 min. A solution of [99mTc(CO)3(H2O)3]+ (900 μl) was added to the vial via syringe and the vial was heated to 70-90° C. for 30 min to yield the corresponding [99mTc(CO)3]+ complexes, [(5)99mTc(CO)3] and [(11)99mTc(CO)3] in high yield via HPLC with radioactive detection. All the results are described in Table 4.












TABLE 4






Nr. of

Temp.
Time



Method
Ligand
Conc. (M)
(° C.)
(min)
Yield (%)




















Two step
5
10−4
70
30
quantitative


labeling
5
10−5
70
30
91[a]



5
10−6
70
30
20[b]



11
10−4
90
30
quantitative[c]



11
5 × 10−5
90
30
quantitative



11
10−5
90
30
quantitative[d]



11
10−6
90
30
41[e]


One pot
11
10−4
90
20
94


labeling
11
5 × 10−5
90
20
96



11
10−5
90
20
34[e]





[a]The labeling was done quantitatively in 1 h. Ligand 5 from the oxidation, at 75° C. for 30 min yield was 85%.


[b]The labeling reached 64% yield after 1.5 h.


[c]Ligand 11 from the oxidation showed 88% yield at 90° C. for 30 min.


[d]Ligand 11 from the oxidation showed 73% yield at 90° C. for 30 min.


[e]The labeling reached more than 65% yield after 1.5 h.

## Claims

1. A compound comprising:
a histidine derivative derivatized at Nε with a constituent comprising a biomolecule, wherein the histidine derivative has a formula (X) or (XV):




wherein BM is a biomolecule, M is radioactive metal, n is an integer from 1 to 5, and X′ is a coupling block selected from the group consisting of —N(H)—C(O)—, —C(O)—N(H)—, —O—P(O−)(O)—O—, —S-halide-, —S-azide-, —S-pseudohalide-, —S-phosphate-, —S-thiol-, —S-silyl-, —O-halide-, —O-azide-, —O-pseudohalide-, —O-phosphate-, —O-thiol-, —O-silyl-, —N(H)-halide-, —N(H)-azide-, —N(H)-pseudohalide-, —N(H)-phosphate-, —N(H)-thiol- and —N(H)-silyl-.

2. The compound of claim 1, wherein the biomolecule is selected from polypeptides, peptides, amino acids, sugars, and vitamins.

3. The compound of claim 1, wherein M is selected from Re, Tc, and Ru.

4. The compound of claim 3, wherein M is selected from 99mTc, 188Re and 97Ru and the radioactively labeled metal tricarbonyl is selected from [99mTc(OH2)3(CO)3]+, [188Re(OH2)3(CO)3]+, and [97Ru(OH2)3(CO)3]2+.

5. The compound of claim 1, wherein the biomolecule is —(CH2)n-COO-pentafluorophenyl.

6. The compound of claim 3, wherein the M is selected from 188Re, 99mTc, and 97Ru.

7. The compound of claim 1, wherein the biomolecule is selected from melanocortin, octreotate, sornastostatin, interleukin-8, CCK, a beta-hairpin loop peptide, neurotensis, biotin, and a monoclonal anti-body.