Selective and predicable amine conjugation sites by kinetic characterization under excess reagents.

The site selectivity for lysine conjugation on a native protein is difficult to control and characterize. Here, we applied mass spectrometry to examine the conjugation kinetics of Trastuzumab-IgG (Her-IgG) and α-lactalbumin under excess linker concentration ([L]0) based on the modified Michaelis-Menten equation, in which the initial rate constant per amine (kNH2 = Vmax/NH2/KM) was determined by the maximum reaction rate (Vmax/NH2) under saturated accessible sites and initial amine-linker affinity (1/KM). Reductive amination (RA) displayed 3-4 times greater Vmax/NH2 and a different panel of conjugation sites than that observed for N-hydroxysuccinimide ester (NHS) chemistry using the same length of polyethylene glycol (PEG) linkers. Moreover, faster conversion power rendered RA site selectivity among accessible amine groups and a greater tunable range of linker/protein ratio for aldehyde-linkers compared to those of the same length of NHS-linkers. Single conjugation with high yield or poly-conjugations with site homogeneity was demonstrated by controlling [L]0 or gradual addition to minimize the [L]0/KM ratio. Formaldehyde, the shortest aldehyde-linker with the greatest 1/KM, exhibited the highest selectivity and was shown to be a suitable probe to predict conjugation profile of aldehyde-linkers. Four linkers on the few probe-predicted hot spots were elucidated by kinetically controlled RA with conserved drug efficacy when conjugated with the payload. This study provides insights into controlling factors for homogenous and predictable amine bioconjugation.

Copper(I)-Catalyzed Nitrile-Addition/N-Arylation Ring-Closure Cascade: Synthesis of 5,11-Dihydro-6H-indolo[3,2-c]quinolin-6-ones as Potent Topoisomerase-I Inhibitors.

In this paper, we present a copper(I)-catalyzed nitrile-addition/N-arylation ring-closure cascade for the synthesis of 5,11-dihydro-6H-indolo[3,2-c]quinolin-6-ones from 2-(2-bromophenyl)-N-(2-cyanophenyl)acetamides. Using CuBr and t-BuONa in dimethylformamide (DMF) as the optimal reaction conditions, the cascade reaction gave the target products, in high yields, with a good substrate scope. Application of the cascade reaction was demonstrated on the concise total syntheses of alkaloid isocryptolepine. Further optimization of the products from the cascade reaction led to 3-chloro-5,12-bis[2-(dimethylamino)ethyl]-5,12-dihydro-6H-[1,3]dioxolo[4',5':5,6]indolo[3,2-c]quinolin-6-one (2k), which exhibited the characteristic DNA topoisomerase-I inhibitory mechanism of action with potent in vitro anticancer activity. Compound 2k actively inhibited ARC-111- and SN-38-resistant HCT-116 cells and showed in vivo activity in mice bearing human HCT-116 and SJCRH30 xenografts. The interaction of 2k with the Top-DNA cleavable complex was revealed by docking simulations to guide the future optimization of 5,11-dihydro-6H-indolo[3,2-c]quinolin-6-ones as topoisomerase-I inhibitors.

Synthesis and antiproliferative activities of ottelione a analogues.

Through the syntheses of its C-1 desvinyl, C-7 methylene, C-7 exocyclic ethylidene, and various C-3 phenylmethyl analogues, the structure-activity relationship of antimitotic ottelione A (4) against tubulin and various cancer cells was established. The results indicated that compound 4 was a colchicine-competitive inhibitor and that the C-1 vinyl group is unnecessary for its potency, whereas the C-7 exocyclic double bond is essential, possibly because of its irreversible interaction with tubulin. Further optimization of the substituents on the phenylmethyl group at the C-3 position generated compound 10g with a 3'-fluoro-4'-methoxyphenylmethyl substituent, which was 6-38-fold more active against MCF-7, NCI-H460, and COLO205 cancer cells relative to 4. Results from in vitro tubulin polymerization assay confirmed the potency of compounds 4, 10g, and 11a.

Synthesis and structure-activity relationship of 3-O-acylated (-)-epigallocatechins as 5α-reductase inhibitors.

A series of 3-O-acylated (-)-epigallocatechins were synthesized and their inhibition of steroid 5α-reductase was studied. They were prepared from the reaction of EGCG with tert-butyldimethylsilyl chloride followed by reductive cleavage of the ester bond. The resultant (-)-epigallocatechins penta-O-tert-butyldimethylsilyl ether was esterified with different fatty acids then desilylated to provide the corresponding products. The activity of 3-O-acylated (-)-epigallocatechins increased with the increasing carbon numbers of the fatty acid moiety, reaching maximum for 16 carbon atoms (compound 4h) with an IC50 of 0.53 µM, which was ∼12-fold more potent than EGCG (IC50=6.29 µM). Introduction of monounsaturated fatty acid provided the most potent compound 6 (IC50=0.48 µM), which showed moderate anti-tumor activity in vivo.

Synthesis of selenophene derivatives as novel CHK1 inhibitors.

A series of selenophene derivatives 3 were synthesized as potential CHK1 inhibitors. The effects of substitution on the 4'- or 5'-position of selenophene moiety and shifting the hydroxyl group position on C6- phenolic ring of oxindole were explored. This study led to the discovery of the most potent CHK1 inhibitors 29-33 and 39-43, which had IC(50) values in the subnanomolar range.

Discovery of pyrrole-indoline-2-ones as Aurora kinase inhibitors with a different inhibition profile.

A series of pyrrole-indolin-2-ones were synthesized, and their inhibition profile for Aurora kinases was studied. The potent compound 33 with phenylsulfonamido at the C-5 position and a carboxyethyl group at the C-3' position selectively inhibited Aurora A over Aurora B with IC50 values of 12 and 156 nM, respectively. Replacement of the carboxyl group with an amino group led to compound 47, which retained the activity for Aurora B and lost activity for Aurora A (IC50=2.19 microM). Computation modeling was used to address the different inhibition profiles of 33 and 47. Compounds 47 and 36 (the ethyl ester analogue of 33) inhibited the proliferation of HCT-116 and HT-29 cells and suppressed levels of the phosphorylated substrates of Aurora A and Aurora B in the Western blots.