Application of novel photoactive iron-N-heterocyclic carbene series compound as photoacoustic contrast agent

Abstract

The invention discloses an iron-N-heterocyclic carbene compound represented by the following general formula (I) and a pharmaceutically acceptable salt thereof, and an application of a pharmaceutical composition containing the compound in preparation of a photoacoustic contrast agent. According to the compound shown in the general formula (I), cheap iron is adopted as a central atom, a series of Fe-NHC molecules with photoacoustic signals in an NIR-II region are constructed, and the Fe-NHC molecules are good in stability and clear and stable in imaging and are brand-new contrast agents. # imgabs0 #

Description

Technical Field

[0001] The invention relates to the fields of medical imaging and pharmaceutical chemistry, and in particular to use of a novel photoactive iron-nitrogen heterocyclic carbene series compound as a photoacoustic contrast agent. Background Art

[0002] Precision treatment of malignant tumors greatly depends on high-resolution, high-quality, multimodal tumor imaging. Photoacoustic imaging is a non-invasive, low-cost imaging technology developed in recent years that can make up for the defects of existing imaging modes and provide diagnostic information that is currently unavailable, such as tissue oxygenation levels, high-resolution vascular network information, etc. It has broad application prospects in the biomedical field. However, optical imaging faces inherent defects. Biological tissues absorb and scatter incident light to varying degrees, causing attenuation of the incident light, thereby reducing the imaging depth and contrast of photoacoustic imaging, which has caused a huge obstacle to the imaging of solid tumors.

[0003] Compared with the visible light and near-infrared I light used in early photoacoustic imaging, the longer wavelength near-infrared II light can effectively increase the tissue penetration depth, increase the maximum allowable irradiation energy, and reduce the biological background noise. In addition, the use of suitable contrast agents can further increase the signal intensity. However, there are relatively few contrast agents that can be used for photoacoustic imaging. Metal-based photoacoustic contrast agents based on cheap metals, such as iron, have not been reported. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a new type of iron-nitrogen heterocyclic carbene compound for use as a photoacoustic contrast agent. Such compound can generate a strong photoacoustic signal under NIR-II region illumination, can be used for photoacoustic imaging, and can be synthesized relatively simply and efficiently.

[0005] On the one hand, an object of the present invention is to provide a class of iron-nitrogen heterocyclic carbene compounds represented by the following general formula (I) and pharmaceutically acceptable salts thereof, as well as the use of pharmaceutical compositions containing such compounds in the preparation of photoacoustic contrast agents:

[0006]

[0007] Wherein, Fe is Fe(III) or Fe(IV),

[0008] n is the number of charges carried by the cation part and the number of anions. When Fe is Fe(III), n=1, and when Fe is Fe(IV), n=2;

[0009] X is an anion required for salt formation, selected from Cl￣, Br￣, I￣, BF4￣, PF6￣, BPh4￣, SO3CF3￣, OAc￣ or OTf￣;

[0010] R1 is hydrogen, substituted or unsubstituted C1-C4 alkyl, substituted or unsubstituted saturated or unsaturated C3-C6 cycloalkyl, substituted or unsubstituted C6-C 10 aryl, substituted or unsubstituted saturated or unsaturated four- to six-membered heterocyclic group containing 1 or 2 heteroatoms selected from N and O, substituted or unsubstituted five- to six-membered heteroaryl group containing 1 or 2 heteroatoms selected from N and O, substituted or unsubstituted C1-C4 alkoxy, substituted or unsubstituted C1-C4 acyl, substituted or unsubstituted C1-C4 alkylamide, substituted or unsubstituted C1-C4 alkylamino, substituted or unsubstituted C1-C4 quaternary ammonium, substituted or unsubstituted C1-C4 ester; wherein the "substituted" means that the group contains 1 or 2 R a The substituent, R a Selected from hydroxy, amino, cyano, nitro, halogen, C1-C3 alkoxy, C1-C3 alkoxycarbonyl, C3-C6 cycloalkyl, phenyl, naphthyl, a saturated or unsaturated four- to six-membered heterocyclic group containing 1 or 2 heteroatoms selected from N and O, and a five- to six-membered heteroaryl group containing 1 or 2 heteroatoms selected from N and O;

[0011] R2 is hydrogen, a halogen atom, an aldehyde group, a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted saturated or unsaturated C5-C6 cycloalkyl group, a phenyl group, a naphthyl group, a substituted or unsubstituted saturated or unsaturated five- or six-membered heterocyclic group containing 1 or 2 heteroatoms selected from N and O, a substituted or unsubstituted five- or six-membered heteroaryl group containing 1 or 2 heteroatoms selected from N and O, a substituted or unsubstituted C1-C3 alkoxy group, or a substituted or unsubstituted C1-C3 acyl group; wherein the "substituted" means that the group contains 1 or 2 R b The substituent, R b Selected from hydroxy, halogen, C1-C3 alkoxy, C5-C6 cycloalkyl, phenyl, naphthyl.

[0012] More preferably, R1 is hydrogen, methyl, ethyl, n-propyl, isopropyl, methoxy, ethoxy, n-propoxy, isopropoxy.

[0013] Preferably, R2 is hydrogen, a halogen atom, an aldehyde group, a substituted or unsubstituted C1-C6 alkyl group, a substituted or unsubstituted saturated or unsaturated C3-C6 cycloalkyl group, a substituted or unsubstituted C6-C 10 aryl, substituted or unsubstituted saturated or unsaturated four- to six-membered heterocyclic group containing 1 or 2 heteroatoms selected from N and O, substituted or unsubstituted five- to eight-membered heteroaryl containing 1 or 2 heteroatoms selected from N and O, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C1-C6 acyl; wherein the "substituted" means that the group contains 1 or 3 R b The substituent, Rb Selected from hydroxyl, halogen, C1-C3 alkoxy, C3-C6 cycloalkyl, C6-C 10 Aryl.

[0014] More preferably, R2 is hydrogen, methyl, ethyl, n-propyl, isopropyl.

[0015] More preferably, X is I￣, BF4￣, PF6￣, BPh4￣, OTf￣.

[0016] More preferably, the compound represented by the general formula (I) according to the present invention and its pharmaceutically acceptable salt are selected from the following compounds:

[0017]

[0018] On the other hand, another object of the present invention is to provide a photoacoustic contrast agent, which comprises an iron-nitrogen heterocyclic carbene compound represented by general formula (I) and a pharmaceutically acceptable salt thereof, or a pharmaceutical composition comprising such a compound, and necessary excipients.

[0019] Beneficial Effects

[0020] The compound represented by the general formula (I) of the present invention uses cheap iron as the central atom to construct a series of Fe-NHC molecules with photoacoustic signals in the NIR-II region. It has good stability, clear and stable imaging, and is a new contrast agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 This is the single crystal diffraction molecular structure diagram of compound LFe-2.

[0023] Figure 2 This is the single crystal diffraction molecular structure diagram of compound LFe-3.

[0024] Figure 3 This is the single crystal diffraction molecular structure diagram of the compound HFe-2.

[0025] Figure 4 This is the single crystal diffraction molecular structure diagram of the compound HFe-3.

[0026] Figure 5 These are the imaging results of compounds LFe-2 and LFe-3.

[0027] Figure 6 These are the imaging results of compounds HFe-1, HFe-2, and HFe-3.

[0028] Figure 7 The relationship between the photoacoustic signal intensity and the concentration of compound HFe-3 is shown.

[0029] Figure 8 This is a comparison chart of the contrast imaging photos of compound HFe-3.

[0030] Fig. 9 Comparison of tumor imaging photos of compound HFe-3. DETAILED DESCRIPTION

[0031] Hereinafter, the present invention will be described in detail. Before describing, it should be understood that the terms used in this specification and the appended claims should not be interpreted as being limited to the general meaning and dictionary meaning, but should be interpreted according to the meaning and concept corresponding to the technical aspects of the present invention on the basis of the principle that the inventor is allowed to appropriately define the terms for the best interpretation. Therefore, the descriptions presented here are only preferred examples for illustrative purposes and are not intended to limit the scope of the present invention, so that it should be understood that other equivalents or improvements can be obtained therefrom without departing from the spirit and scope of the present invention.

[0032] In this document, the terms "include", "including", "have", "contain" or any other similar terms are open conjunctions, which are intended to cover non-exclusive inclusions. For example, a composition or product containing multiple elements is not limited to the elements listed herein, but may also include other elements that are not explicitly listed but are generally inherent to the composition or product. In addition, unless otherwise explicitly stated, the term "or" refers to an inclusive "or" rather than an exclusive "or". For example, any of the following situations satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), and A and B are both true (or exist). In addition, in this document, the interpretation of the terms "include", "including", "have", and "contain" should be considered to have been specifically disclosed and simultaneously cover closed or semi-closed conjunctions such as "consisting of" and "consisting essentially of".

[0033] In this article, all features or conditions defined in the form of numerical ranges or percentage ranges are only for brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be deemed to have covered and specifically disclosed all possible secondary ranges and individual values ​​within the range, especially integer values. For example, the range description of "1 to 8" should be deemed to have specifically disclosed all secondary ranges such as 1 to 7, 2 to 8, 2 to 6, 3 to 6, 4 to 8, 3 to 8, etc., especially secondary ranges defined by all integer values, and should be deemed to have specifically disclosed individual values ​​such as 1, 2, 3, 4, 5, 6, 7, 8, etc. within the range. Unless otherwise specified, the above interpretation method applies to all contents of the entire present invention, regardless of whether the range is broad or not.

[0034] If the quantity or other numerical value or parameter is expressed as a range, a preferred range or a series of upper and lower limits, it should be understood that all ranges consisting of any upper limit or preferred value of the range and the lower limit or preferred value of the range have been specifically disclosed herein, regardless of whether these ranges are disclosed separately. In addition, if a numerical range is mentioned herein, unless otherwise specified, the range should include its endpoints and all integers and fractions within the range.

[0035] In this document, under the premise of achieving the purpose of the invention, numerical values ​​should be understood to have the accuracy of the number of significant digits of the numerical value. For example, the number 40.0 should be understood to cover the range from 39.50 to 40.49.

[0036] In this article, for the use of Markush groups or optional terms to describe the features or examples of the present invention, those skilled in the art should understand that all subgroups of elements in the Markush group or option list or any individual element can also be used to describe the present invention. For example, if X is described as "selected from the group consisting of X1, X2 and X3", it also means that the claim that X is X1 and the claim that X is X1 and / or X2 have been fully described. Furthermore, for the use of Markush groups or optional terms to describe the features or examples of the present invention, those skilled in the art should understand that any combination of all subgroups of elements in the Markush group or option list or individual elements can also be used to describe the present invention. Accordingly, for example, if X is described as "selected from the group consisting of X1, X2 and X3", and Y is described as "selected from the group consisting of Y1, Y2 and Y3", it means that the claim that X is X1 or X2 or X3 and Y is Y1 or Y2 or Y3 has been fully described.

[0037] The following examples are only listed as examples of embodiments of the present invention and do not constitute any limitation to the present invention. It can be understood by those skilled in the art that modifications within the scope of the essence and concept of the present invention fall within the scope of protection of the present invention. Unless otherwise specified, the reagents and instruments used in the following examples are all commercially available products.

[0038] Example 1. 1,1'-(5-methoxy-1,3-phenylene)bis(1H-imidazole) (Compound A)

[0039]

[0040] The diimidazole substituted compound was synthesized by an Ullmann-type reaction similar to that reported in the literature (CuI / L(L1 / 4pyridine-functionalized 1,3-diketones)catalyzed CeN coupling reactions of aryl halides with NH-containingheterocycles, Tetrahedron 64(2008)4254-4259, DOI:10.1016 / j.tet.2008.02.082). 5mmol of 3,5-dibromoanisole, 25mmol of imidazole, 2mmol of N,N-dimethylglycine, 25mmol of K2CO3 and 1mmol of CuI were added to a 100mL round-bottom flask with a magnetic stirrer. The flask was evacuated and refilled with nitrogen three times, and then 20mL of dimethyl sulfoxide was added under N2 flow. After the reaction was completed, the reactant was poured into dichloromethane and washed with water three times. The organic phase was dried over Na2SO4, and the solvent was evaporated on a rotary evaporator to obtain a crude product. The crude product was purified by column chromatography (silica gel, DCM:MeOH=200:1 to 20:1) to obtain pure compound A as a white solid in a yield of 82%.

[0041] 1 H NMR (400MHz, DMSO-d6) δ8.42(t,J=1.2Hz,1H),7.91(t,J=1.4Hz,1H),7.56(t,J=1.9Hz,1H),7.24(d,J=1.9Hz,1H),7.13(t,J=1.2Hz,1H),3.91(s,2H).

[0042] 13 C NMR (101MHz, DMSO-d6) δ161.32,138.87,135.86,129.90,118.16,104.08,56.06.

[0043] HRMS(ESI):m / z=calculated for[M+H] + :241.1084; Found:[M+H] + :241.1071.

[0044] Example 2. 1,1'-(5-methoxy-1,3-phenylene)bis(3-methyl-1H-imidazol-3-ium) diiodide (Compound C)

[0045]

[0046] Under N2 atmosphere, 2mmol of 1,1'-(5-methoxy-1,3-phenylene)bis(1H-imidazole) was dissolved in a mixture of 1mL of CH3I and 5mL of MeCN, and heated under reflux for 24 hours. After the reaction, the reactant was poured into methyl tert-butyl ether, filtered, and the filter cake was washed with methyl tert-butyl ether and dried to obtain a yellow solid compound C with a yield of 91%.

[0047] 1 H NMR (400MHz, DMSO-d6) δ9.89(s,2H),8.37(s,2H),8.02(s,2H),7.87(t,J=1.5Hz,1H),7.63(d,J=1.9Hz,2H),3.99(s,6H),3.98(s,3H).

[0048] 13 C NMR (101MHz, DMSO-d6) δ161.18,136.52,136.39,124.64,108.56,107.15,56.87,36.45.

[0049] HRMS(ESI):m / z=calculated for[C 15 H 18 N4O] 2+ :135.0735;Found:[C 15 H 18 N4O] 2+ :135.0726.

[0051] Example 3. 1,1'-(5-morpholinyl-1,3-phenylene)bis(3-methyl-1H-imidazol-3-ium) diiodide (Compound D)

[0052]

[0053] The light yellow solid compound D was prepared according to the method of Example 2 with a yield of 75%, except that 2 mmol of 4-(3,5-di(1H-imidazol-1-yl)phenyl)morpholine was used instead of 1,1'-(5-methoxy-1,3-phenylene)bis(1H-imidazole).

[0054] Compound D:

[0055] 1 H NMR (400MHz, DMSO-d6) δ9.84(s,2H),8.33(t,J=1.9Hz,2H),8.00(t,J=1.8Hz,2H),7.57(t,J= 1.8Hz,1H),7.45(d,J=1.8Hz,2H),3.98(s,6H),3.80(t,J=4.8Hz,4H),3.40(t,J=4.9Hz,4H).

[0056] 13 C NMR (101MHz, DMSO-d6) δ152.75,136.64,136.27,124.59,120.90,107.56,103.90,65.67,47.42,36.42.

[0057] HRMS(ESI):m / z=calculated for[C 18 H 23 N5O] 2+ :162.5946;Found:[C 18 H 23 N5O] 2+ :162.5935.

[0059] Example 4. Preparation of compound LFe-2

[0060]

[0061] In an argon-filled glove box, 2mmol of 1,1'-(5-methoxy-1,3-phenylene)bis(3-methyl-1H-imidazole-3-ium) diiodide was added to a 50mL round-bottom flask containing 5mL of dry THF. Then 42.1mmol of Zr(NMe2) and 2mmol of FeCl2 were added, and stirring continued at room temperature overnight. After the reaction was completed, the system was exposed to air, 10mL of MeCN and 1mL of H2O were added, and stirred for 0.5 hours. The suspension was filtered and washed with acetonitrile until the filtrate had no obvious color. The volatiles were removed in vacuo. The obtained solid was dissolved in MeOH, and 5mL of saturated KPF6 solution and 10mL of H2O were added to precipitate it. The precipitate was filtered, rinsed with H2O and dried to obtain compound 1 as a cyan powder with a yield of 45%.

[0062] Compound LFe-2:

[0063] HRMS(ESI):m / z=calculated for[Fe] + :590.1836; Found:[Fe] + :590.1824.

[0064] Figure 1 This is the single crystal diffraction molecular structure diagram of compound LFe-2.

[0065] Example 5. Preparation of compound LFe-3

[0066]

[0067] The green solid compound LFe-3 was prepared in the same manner as in Example 5, except that 2 mmol of 4-(3,5-di(1H-imidazol-1-yl)phenyl)morpholine was used instead of 1,1′-(5-methoxy-1,3-phenylene)bis(1H-imidazole) in a yield of 41%.

[0068] Compound LFe-3:

[0069] HRMS(ESI):m / z=calculated for[Fe] + :890.3501; Found:[Fe] + :890.3475.

[0070] Figure 2 This is the single crystal diffraction molecular structure diagram of compound LFe-3.

[0071] Example 6. Preparation of Compound HFe-1

[0072]

[0073] In an argon-filled glove box, 2mmol of 1,1'-(1,3-phenylene)bis(3-methyl-1H-imidazol-3-ium) diiodide was added to a 50mL round-bottom flask containing 5mL of dry THF. Then, 2.1mmol of Zr(NMe2)4 and 2mmol of FeCl2 were added, and stirring continued overnight at room temperature. After the reaction was completed, the system was exposed to air, 10mL of MeCN and 1mL of H2O were added, and stirred for 0.5 hours. The suspension was filtered and washed with acetonitrile until the filtrate had no obvious color. The volatiles were removed in vacuo. The obtained solid was dissolved in MeOH, and 5mL of saturated KPF6 solution and 10mL of H2O were added to precipitate it. The precipitate was filtered, rinsed with H2O and dried to obtain a dark purple powder. The powder was dissolved in a round bottle containing 5mmol of KPF6 and 5mL of methanol. 0.5 mL of 10% H2O2 solution was added dropwise, followed by stirring at room temperature overnight, and then 10 mL of H2O was added to precipitate. The precipitate was filtered, washed with H2O to remove inorganic salts, and dried to obtain a brown solid compound HFe-1 with a total yield of 38%.

[0074] HRMS(ESI):m / z=calculated for[Fe] 2+ :265.0809; Found:[Fe] 2+ :265.0800.

[0075] Example 7. Preparation of Compound HFe-2

[0076]

[0077] Add 0.5 mmol of compound LFe-2 into a round bottle containing 5 mmol of KPF6 and 5 mL of methanol. Add 0.5 mL of 10% H2O2 solution dropwise. Stir the reaction solution at room temperature overnight, then add 10 mL of H2O to precipitate it. Filter the precipitate, wash away the inorganic salt with H2O, and dry it to obtain a dark red solid compound HFe-2 with a yield of 90%.

[0078] 1 H NMR (400MHz, DMSO-d6) δ51.70(s,6H),35.49(s,12H),18.54(s,4H),12.83(s,4H),-27.33(s,4H).

[0079] HRMS(ESI):m / z=calculated for[Fe] 2+ :350.1337; Found:[Fe] 2+ :350.1330.

[0080] Figure 3 This is the single crystal diffraction molecular structure diagram of the compound HFe-2.

[0081] Example 8. Preparation of compound HFe-3

[0082]

[0083] Add 0.5 mmol of compound LFe-3 to a round bottle containing 5 mmol of KPF6 and 5 mL of methanol. Add 0.5 mL of 10% H2O2 solution dropwise. Stir the reaction solution at room temperature overnight, then add 10 mL of H2O to precipitate it. Filter the precipitate, wash away the inorganic salt with H2O, and dry it to obtain a dark red solid compound HFe-3 with a yield of 90%.

[0084] 1 H NMR (400MHz, DMSO-d6) δ27.13(s,16H),10.80(s,4H),1.98(s,12H),-20.47(s,4H),-31.23(s,4H).

[0085] HRMS(ESI):m / z=calculated for[Fe] 2+ :350.1337; Found:[Fe] 2+ :350.1330.

[0086] Figure 4 The single crystal diffraction molecular structure diagram of compound HFe-3. The single crystal diffraction data of compounds LFe-2, HFe-2, LFe-3, and HFe-3 are shown in Table 1 below.

[0087] Table 1. Crystal data and structural analysis of compounds LFe-2, HFe-2, LFe-3, and HFe-3

[0088]

[0089]

[0090]

[0091]

[0092]

[0093]

[0094] Test Example 1 In vitro contrast imaging

[0095] The compounds LFe-2 and LFe-3 prepared in Examples 4, 5 and 6 were prepared into 10 uM solutions using commercial PBS buffer (Gibco). The solutions were filled into plastic tubes and placed in a TomoWave 3D photoacoustic imager. The imaging results were recorded under 808 pulse lasers. Figure 5 As shown, the left picture is the longitudinal section of the solution, and the right picture is the cross section. It can be seen that both contrast agents can be imaged clearly and have good signal intensity.

[0096] Test Example 2 In vitro contrast imaging

[0097] The in vitro contrast imaging test of the compounds HFe-1, HFe-2 and HFe-3 prepared in Examples 7, 8 and 9 was carried out in the same manner as in Test Example 1. The laser wavelength used for imaging was 1064 nm. The imaging results are shown in FIG. Figure 6 As shown, the Fe core in HFe-1, HFe-2, and HFe-3 is oxidized to a valence of 4.

[0098] Figure 6 To test the imaging results of HFe-1, HFe-2, and HFe-3 in Example 2, from left to right are: HFe-1, HFe-2, and HFe-3 solutions, the left picture is the longitudinal section of the solution, and the right picture is the cross section. It can be seen that under the near-infrared laser in the NIR-II region, HFe-3 can still obtain high-intensity imaging signals, while HFe-1 and HFe-2 are unusable at this wavelength and have no signals.

[0099] Relationship between the intensity of photoacoustic signal and the concentration of compound HFe-3 in test example 3

[0100] Commercial PBS buffer (Gibco) was used to prepare 20uM, 40uM, 80uM HFe-3 compound solutions, as well as pure PBS solution. The same instrument as in Test Example 1 was used to perform photoacoustic imaging on this series of solutions (the upper row of circles in the figure below), and the photoacoustic signal intensity was measured.

[0101] The results are as follows Figure 7 As shown, there is no signal at 1064 nm for pure PBS solution as a solvent, while the photoacoustic signal intensity of HFe-3 solution with a concentration of 20uM-80uM shows a good linear relationship with the compound concentration.

[0102] Test Example 4 Angiographic Imaging

[0103] The mouse tail vein was injected with 100ul of 50uM compound HFe-3 in PBS solution, and photoacoustic imaging was performed 10 minutes later. Compared with before injection, the photoacoustic signal in the mouse blood vessels was enhanced; half an hour later, the kidney signal was significantly enhanced, and the distribution of fine structures was visible. The results are as follows Figure 8 As shown, Figure 8 From left to right in the figure are the contrast imaging photos before injection, 10 minutes after injection, and 30 minutes after injection. It can be seen that after the injection of the compound, the signal in the blood vessels of the mouse was significantly enhanced through the renal section imaging, and the tissue contrast was deepened.

[0104] Test Example 5 Tumor Imaging

[0105] The BALB / C mice used in the study were purchased from the Hubei Provincial Center for Disease Control and Prevention and were raised in a specific pathogen-free animal experiment. Mouse blood was collected using a blood collection tube containing EDTA anticoagulant, and red blood cells were separated by centrifugation at 800rpm for 10 minutes. The supernatant was centrifuged at 20,000 rpm to obtain platelets. The obtained platelets were frozen at -80 degrees Celsius, then thawed in a 37-degree Celsius water bath, and repeated three times to obtain platelet membranes. HFe-3 solution (50uM, dissolved in PBS) was added, and the platelet membrane-loaded compound HFe-3 was prepared using an Avanti micro-extruder and a 200nm pore size membrane. 4T1 cells were inoculated subcutaneously on the right back of the mouse, with 10^6 cells inoculated per mouse. It can be seen that there is a strong photoacoustic signal in the tumor area of ​​the mouse after 6 hours, proving that the drug accumulates in the tumor to achieve the purpose of imaging the tumor site. The results are as follows Fig. 9 As shown, Fig. 9 The left picture in the middle is before injection, and the right picture is 6 hours after injection. It can be seen from the picture that the mouse tumor has obvious photoacoustic signals after injection, indicating that the compound HFe-3 accumulates in the tumor.

[0106] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. Use of an iron-nitrogen heterocyclic carbene compound represented by the following general formula (I) and a pharmaceutically acceptable salt thereof, and a pharmaceutical composition comprising the compound in the preparation of a photoacoustic contrast agent: in, Fe is Fe(III) or Fe(IV), n is the number of charges carried by the cation part and the number of anions. When Fe is Fe(III), n=1, and when Fe is Fe(IV), n=2; X is an anion required for salt formation, selected from Cl￣, Br￣, I￣, BF4￣, PF6￣, BPh4￣, SO3CF3￣, OAc￣ or OTf￣; R1 is hydrogen, substituted or unsubstituted C1-C4 alkyl, substituted or unsubstituted saturated or unsaturated C3-C6 cycloalkyl, substituted or unsubstituted C6-C 10 aryl, substituted or unsubstituted saturated or unsaturated four- to six-membered heterocyclic group containing 1 or 2 heteroatoms selected from N and O, substituted or unsubstituted five- to six-membered heteroaryl group containing 1 or 2 heteroatoms selected from N and O, substituted or unsubstituted C1-C4 alkoxyl group, substituted or unsubstituted C1-C4 acyl group, substituted or unsubstituted C1-C4 alkylamide group, substituted or unsubstituted C1-C4 alkylamino group, substituted or unsubstituted C1-C4 quaternary ammonium group, substituted or unsubstituted C1-C4 ester group; wherein the "substituted" means that the group contains 1 or 2 R a The substituent, R a Selected from hydroxy, amino, cyano, nitro, halogen, C1-C3 alkoxy, C1-C3 alkoxycarbonyl, C3-C6 cycloalkyl, phenyl, naphthyl, a saturated or unsaturated four- to six-membered heterocyclic group containing 1 or 2 heteroatoms selected from N and O, and a five- to six-membered heteroaryl group containing 1 or 2 heteroatoms selected from N and O; R2 is hydrogen, a halogen atom, an aldehyde group, a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted saturated or unsaturated C5-C6 cycloalkyl group, a phenyl group, a naphthyl group, a substituted or unsubstituted saturated or unsaturated five- or six-membered heterocyclic group containing 1 or 2 heteroatoms selected from N and O, a substituted or unsubstituted five- or six-membered heteroaryl group containing 1 or 2 heteroatoms selected from N and O, a substituted or unsubstituted C1-C3 alkoxy group, or a substituted or unsubstituted C1-C3 acyl group; wherein the "substituted" means that the group contains 1 or 2 R b The substituent, R b Selected from hydroxy, halogen, C1-C3 alkoxy, C5-C6 cycloalkyl, phenyl, naphthyl.

2. The use according to claim 1, characterized in that R1 is hydrogen, methyl, ethyl, n-propyl, isopropyl, methoxy, ethoxy, n-propoxy, isopropoxy.

3. The use according to claim 1, characterized in that R2 is hydrogen, a halogen atom, an aldehyde group, a substituted or unsubstituted C1-C6 alkyl group, a substituted or unsubstituted saturated or unsaturated C3-C6 cycloalkyl group, a substituted or unsubstituted C6-C 10 aryl, substituted or unsubstituted saturated or unsaturated four- to six-membered heterocyclic group containing 1 or 2 heteroatoms selected from N and O, substituted or unsubstituted five- to eight-membered heteroaryl containing 1 or 2 heteroatoms selected from N and O, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C1-C6 acyl; wherein the "substituted" means that the group contains 1 or 3 R b The substituent, R b Selected from hydroxyl, halogen, C1-C3 alkoxy, C3-C6 cycloalkyl, C6-C 10 Aryl; More preferably, R2 is hydrogen, methyl, ethyl, n-propyl, isopropyl.

4. The use according to claim 1, characterized in that X is I￣, BF4￣, PF6￣, BPh4￣, OTf￣.

5. The use according to claim 1, characterized in that: The compound represented by general formula (I) and its pharmaceutically acceptable salt are selected from the following compounds:

6. A photoacoustic contrast agent, comprising the iron-nitrogen heterocyclic carbene compound represented by general formula (I) and its pharmaceutically acceptable salt or a pharmaceutical composition containing such compound in the use according to claim 1, and necessary excipients.

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