Here we present an evaluation of the binding affinity prediction accuracy of the free energy calculation method FEP+ on internal active drug discovery projects and on a large new public benchmark set. File list (3) download file view on ChemRxiv manuscript.pdf (4.23 MiB) download file view on ChemRxiv supplementary.pdf (0.92 MiB) download file view on ChemRxiv tables.zip (5.99 KiB)

Recent progress in the synthesis of water-soluble phosphine ligand systems and their corresponding 99mTc complexes prompted the development of a new bifunctional chelating agent (BFCA) based on a tetradentate dithiadiphosphine framework (P2S2-COOH). The detailed synthesis of this new BFCA is described here. The corresponding 99mTc complex, 99mTc-P2S2-COOH, can be formed in >95% yield. To demonstrate the potential of this chelate to efficiently label peptides, 99mTc-P2S2-COOH was coupled to the N-terminal region of the truncated nine-amino acid bombesin analogue, 5-Ava-Gln-Trp-Ala-Val-Gly-His-Leu-Met-NH2 [BBN(7-14)], to form 99mTc-P2S2-BBN(7-14). Conjugation to the peptide was performed in borate buffer (pH 8.5) by applying the prelabeling approach in yields of >60%. In competitive binding assays, using Swiss 3T3 mouse fibroblast cells against [125I-Tyr4]bombesin, Re-P2S2-BBN(7-14) exhibited an IC50 value of 0.8 +/- 0.4 nM. The pharmacokinetic studies of 99mTc-P2S2-BBN(7-14) and its ability to target tissue expressing gastrin-releasing peptide (GRP) receptors were performed in normal mice. The 99mTc-P2S2-BBN(7-14) exhibited fast and efficient clearance from the blood pool (0.6 +/- 0.1% ID, 4 h postinjection) and excretion through the renal and hepatobiliary pathways (56.4 +/- 8.2 and 28.1 +/- 7.9% ID, 4 h postinjection, respectively). Significant uptake in the pancreas was observed (pancreatic acini cells express bombesin/GRP receptors), producing pancreas:blood and pancreas:muscle ratios of ca. 22 and 80, respectively, at 4 h postinjection.

Here we present an evaluation of the binding affinity prediction accuracy of the free energy calculation method FEP+ on internal active drug discovery projects and on a large new public benchmark set.<br>

The nucleophile-assisted ring-opening reaction of phthalimides 1 has been studied. The reaction of phthalimides 1 with 0.5 equiv of hydrazine produced the novel bisphosphonates 2 in near quantitative yields whereas with 10-fold excess of hydrazine, diethyl aminoalkylphosphonates 3 was formed in 75% yields. The reaction of phthalimide 1b with 3-(aminopropyl)phosphine resulted in a novel compound 4a containing a PIII hydride and a PV phosphonate within the same molecule. In addition, the reaction of 1b with 2-aminoethanol and 2-aminoethanethiol resulted in the formation of new phosphonates 4b,c. The reaction of bisphosphonates 2 with LiAlH4 in THF at 0 °C selectively reduced the phosphonate groups producing corresponding air-stable primary bisphosphines 6 in 80% yields. Further, the formylation of bisphosphines 6 under very mild conditions using 37% aqueous formaldehyde produced the corresponding novel water-soluble bisphosphine chelating agents 7 in near quantitative yields. All the new compounds have been characterized by 1H, 13C, 31P NMR, IR spectroscopy and mass spectrometry.

The thioether-functionalized, water-soluble, bis(phosphines) (HOH(2)C)(2)PCH(2)CH(2)S(CH(2))(3)SCH(2)CH(2)P(CH(2)OH)(2) (9) and C(6)H(4){1,2-SCH(2)CH(2)P(CH(2)OH)(2)}(2) (10) were synthesized in near quantitative yields by the formylation of the appropriate phosphine hydrides in the presence of formaldehyde in ethanol. The reactions of 9 and 10 with Pt(COD)Cl(2) and Pd(C(6)H(5)CN)(2)Cl(2) in biphasic media (aqueous/organic) produced the water-soluble Pt(II) and Pd(II) complexes [Pt(HOH(2)C)(2)P(CH(2))(2)S(CH(2))(3)S(CH(2))(2)P(CH(2)OH)(2)](Cl)(2) (11), [Pd(HOH(2)C)(2)P(CH(2))(2)S(CH(2))(3)S(CH(2))(2)P(CH(2)OH)(2)](Cl)(2) (12), [Pt{(C(6)H(4)){1,2-S(CH(2))(2)P(CH(2)OH)(2)}(2)}](Cl)(2) (13), and [Pd{(C(6)H(4)){1,2-S(CH(2))(2)P(CH(2)OH)(2)}(2)}](Cl)(2) (14) in near quantitative yields. The X-ray crystal structure of 12 confirms a square-planar Pd(II) structure for this new generation of water-soluble transition metal complexes. All of the complexes were characterized by MS, (1)H, (13)C, and (31)P NMR spectroscopy. X-ray data for 12: triclinic, P&onemacr;, a = 9.9761(6) Å, b = 10.2049(7) Å, c = 11.6954(7) Å, alpha = 67.730(10) degrees, beta = 69.943(10) degrees, gamma = 79.828(10) degrees, Z = 2, R = 0.0307 (R(w) = 0.0797).

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The efficiency of photolabeling of HSA and IgG with [14C]methyl 4-azido-2,3,5,6-tetrafluorobenzoate has been studied using size exclusion chromatography in conjunction with liquid scintillation counting. Labeling efficiencies of 78% for HSA and 82% for IgG have been determined. The extent of bond insertion into proteins exceeds the C-H insertion efficiency in cyclohexane with less wastage into anilinium and azo side products. These results suggest that the photoprobe accesses hydrophobic regions of both proteins prior to photolysis.

Synthesis and evaluation of a new class of photochemically activated heterobifunctional chelating agents for protein modification is described. Selective functionalization of perfluoroaryl azides by versatile phosphorus hydrazide ligating systems 2 and 3 for the complexation of transition metals and analogous radiometals form the basis for these new agents. The utility of the photogenerated precursors from these bifunctional agents to form covalent attachments is demonstrated through examination of C-H bond insertion on cyclohexane. Representative amide-coupled phosphorus hydrazides 5 and 6 provide >78% insertion of the probe into unactivated C-H bonds of cyclohexane with short photolysis times. Photoconjugation of the photoactivable heterobifunctional chelating agent 6 and its Pd metalated analog 7 with HSA is also evaluated. The uncomplexed chelate appears to add to HSA with high efficiency, consistent with the observed 82% bond insertion into model solvents. Covalent attachment of 7, evaluated through the use of (109)Pd, was estimated to be between 49% and 74% with the uncertainty arising because of prephotolysis association of the (109)Pd complex with HSA. The application of in situ (19)F NMR to distinguish between bond insertion and noninsertion processes is demonstrated. These results suggest that functionalized perfluoroaryl azido phosphorus hydrazides may find utility as heterobifunctional photolabeling agents for attaching radionuclides to proteins and antibodies.