Reaction SMILES: C(O)[C@H]1O[C@H](O[C@H]2[C@H](O)[C@@H](O)[C@H](O)O[C@@H]2CO)[C@H](O)[C@@H](O)[C@@H]1O.[Sn].O=C1O[C@H]([C@H](CO)O)C(O)=C1O.[CH3:37][CH:38]([C@@H:40]1[NH:64][C:62](=[O:63])[C@H:61]([CH2:65][CH2:66][CH2:67][CH2:68][NH2:69])[NH:60][C:58](=[O:59])[C@H:57]([CH2:70][C:71]2[C:75]3[CH:76]=[CH:77][CH:78]=[CH:79][C:74]=3[NH:73][CH:72]=2)[NH:56][C:54](=[O:55])[C@@H:53]([CH2:80][C:81]2[CH:82]=[CH:83][C:84]([OH:87])=[CH:85][CH:86]=2)[NH:52][C:50](=[O:51])[C@@H:49]([NH:88][C:89]([C@H:91]([NH2:99])[CH2:92][C:93]2[CH:94]=[CH:95][CH:96]=[CH:97][CH:98]=2)=[O:90])[CH2:48][S:47][S:46][CH2:45][C@@H:44]([C:100]([NH:102][C@H:103]([C:114]([NH2:116])=[O:115])[CH2:104][C:105]2[C:109]3[CH:110]=[CH:111][CH:112]=[CH:113][C:108]=3[NH:107][CH:106]=2)=[O:101])[NH:43][C:41]1=[O:42])[CH3:39].CC(O)=O.O=C1O[C@H]([C@H](CO)O)C([O-])=C1O.C(O)=C>C(C(C(C([O-])=O)O)O)([O-])=O.[K+].[Na+].C(O)(=O)C1C(=CC=CC=1)C([O-])=O.[K+]>[NH2:99][C@@H:91]([C:89]([NH:88][C@H:49]([C:50]([NH:52][C@H:53]([C:54]([NH:56][C@@H:57]([C:58]([NH:60][C@H:61]([C:62]([NH:64][C@H:40]([C:41]([NH:43][C@H:44]([C:100]([NH:102][C@H:103]([C:114]([NH2:116])=[O:115])[CH2:104][C:105]1[C:109]2[C:108](=[CH:113][CH:112]=[CH:111][CH:110]=2)[NH:107][CH:106]=1)=[O:101])[CH2:45][SH:46])=[O:42])[CH:38]([CH3:37])[CH3:39])=[O:63])[CH2:65][CH2:66][CH2:67][CH2:68][NH2:69])=[O:59])[CH2:70][C:71]1[C:75]2[C:74](=[CH:79][CH:78]=[CH:77][CH:76]=2)[NH:73][CH:72]=1)=[O:55])[CH2:80][C:81]1[CH:82]=[CH:83][C:84]([OH:87])=[CH:85][CH:86]=1)=[O:51])[CH2:48][SH:47])=[O:90])[CH2:92][C:93]1[CH:94]=[CH:95][CH:96]=[CH:97][CH:98]=1
Reactant: CC(C)[C@@H]1NC(=O)[C@H](CCCCN)NC(=O)[C@H](Cc2c[nH]c3ccccc23)NC(=O)[C@@H](Cc2ccc(O)cc2)NC(=O)[C@@H](NC(=O)[C@H](N)Cc2ccccc2)CSSC[C@@H](C(=O)N[C@@H](Cc2c[nH]c3ccccc23)C(N)=O)NC1=O
Agent: C=CO
Agent: O=C([O-])C(O)C(O)C(=O)[O-]
Agent: O=C([O-])c1ccccc1C(=O)O
Solvent: CC(=O)O
Product: CC(C)[C@H](NC(=O)[C@H](CCCCN)NC(=O)[C@@H](Cc1c[nH]c2ccccc12)NC(=O)[C@H](Cc1ccc(O)cc1)NC(=O)[C@H](CS)NC(=O)[C@H](N)Cc1ccccc1)C(=O)N[C@@H](CS)C(=O)N[C@@H](Cc1c[nH]c2ccccc12)C(N)=O
Reaction time: 0.75 h

Procedure:
Radiolabeling kits were prepared using aseptic techniques, with each kit prepared in a 10 ml serum vial using a 2 ml liquid fill. The liquid fill contained 200 μg of RC-160 peptide in 45 mM sodium potassium tartrate, 10 mM potassium hydrogen phthalate buffer, pH 5.0, in 5 mM stannous tartrate with 1% maltose added as a freeze-drying excipient. Each kit contained a maximum of 1.19 μg of tin. After filling, the vials were lyophilized, the head space gas filled with nitrogen, and the vials stoppered and crimped. Lyophilized vials were then stored refrigerated at 2-8° C. To label a kit, 4-5 ml of 188Re-perrhenate solution containing 10-100 mCi was added to the kits, and the kits then heated in a boiling water bath for 30-45 minutes. Following a brief cooling period, 2 ml of ascorbic acid for Injection, U.S.P., was added to the labeled kit through a 0.22 micron filter. Two types of parenteral ascorbate were used with similar results, Ascorbic Acid for Injection, U.S.P., 500 mg/2 ml, and Ascorvit™ (a preparation of ascorbate) 100 mg (Jenapharm, Germany). An elution profile from an analytical IPLC at 6-hours post-labeling is shown in FIG. 1. In this study, RC-160 was radiolabeled at pH 5.0 for 30 minutes at 90° C. and ascorbate was added post-labeling. The temperature effect is shown in FIG. 2: 19 minutes for 37° C. and 21 minutes for 90° C. Also shown in FIG. 1 as an inset is an elutiori profile of Re-188-RC 160 from a C18 column using a step-gradient of acidified ethenol. The results are consistent with the HPLC. 188Re-RC-160 to which ascorbate was not added was found to be stable for only up to two hours post-labeling; however, after that the 188Re began to uncouple from the peptide as determined by TLC (using silica-coated thin layer chromatography strips) and confirmed by RP-HPLC (analytical reverse phase HPLC using a C18 column eluted with a continuous gradient of acetonitrile and analyzed by a post-column radioisotope detector, generally at a flow rate of 1 ml/minute). This uncoupling occurred with 188Re, but not with Tc-99m when used in the same amounts, 20 mCi, suggesting the effect was specific to rhenium at his particular concentration. Post-labeling addition of ascorbate was found to essentially eliminate the uncoupling and stabilize the 188Re-RC-160. FIG. 6. An HPLC profile at 30 hours post-labeling with 65 mCi of 188Re to which ascorbate was added after labeling demonstrated that very little free rhenium could be found. FIG. 7 and FIG. 1. Cysteine displacement studies demonstrated that the Re-peptide bond strength was not altered by addition of the ascorbate post-labeling. Briefly, aliquots of 100 μl cysteine dissolved in phosphate buffer saline (pH 7.4 with 1 M NaOH) were diluted in separate microfuge tubes to result in a doubling dilution. 100 μl of Re188-RC-160 was added to each tube and mixed by inversion. The samples were incubated at 45 minutes at 37° C. or 90° C. A 10 μl aliquot of each sample was then spotted on heat-treated ITC strip and chromatographed in PBS, pH 7-4 until the solvent was 0.5 cm from the strip top. The amount of displacement was expressed as % of total radioactivity at the solvent front.