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The Wittig reaction can be used for late stage functionalization of proteins and peptides to ligate glycans, pharmacophores, and many other functionalities. In this manuscript, we modified 160 000 N-terminal glyoxaldehyde peptides displayed on phage with the Wittig reaction by using a biotin labeled ylide under conditions that functionalize only 1% of the library population. Deep-sequencing of the biotinylated and input populations estimated the rate of conversion for each sequence. This “deep conversion” (DC) from deep sequencing correlates with rate constants measured by HPLC. Peptide sequences with fast and slow reactivity highlighted the critical role of primary backbone amides (N–H) in accelerating the rate of the aqueous Wittig reaction. Experimental measurement of reaction rates and density functional theory (DFT) computation of the transition state geometries corroborated this relationship. We also collected deep-sequencing data to build structure–activity relationship (SAR) models that can predict the DC value of the Wittig reaction. By using these data, we trained two classifier models based on gradient boosted trees. These classifiers achieved area under the ROC (receiver operating characteristic) curve (ROC AUC) of 81.2 ± 0.4 and 73.7 ± 0.8 (90–92% accuracy) in determining whether a sequence belonged to the top 5% or the bottom 5% in terms of its reactivity. This model can suggest new peptides never observed experimentally with ‘HIGH’ or ‘LOW’ reactivity. Experimental measurement of reaction rates for 11 new sequences corroborated the predictions for 8 of them. We anticipate that phage-displayed peptides and related mRNA or DNA-displayed substrates can be employed in a similar fashion to study the substrate scope and mechanisms of many other chemical reactions., 160 000 peptides displayed on phage were subjected to the Wittig reaction with a biotinylated ylide. Deep-sequencing estimated the conversion rate for each sequence and unveiled the relationship between sequences and the rate of the Wittig reaction.

In this manuscript, we developed a two-fold symmetric linchpin (TSL) that converts readily available phage-displayed peptides libraries made of 20 common amino acids to genetically-encoded libraries of bicyclic peptides displayed on phage. TSL combines an aldehyde-reactive group and two thiol-reactive groups; it bridges two side chains of cysteine [C] with an N-terminal aldehyde group derived from the N-terminal serine [S], yielding a novel bicyclic topology that lacks a free N-terminus. Phage display libraries of SX1CX2X3X4X5X6X7C sequences, where X is any amino acid but Cys, were converted to a library of bicyclic TSL-[S]X1[C]X2X3X4X5X6X7[C] peptides in 45 ± 15% yield. Using this library and protein morphogen NODAL as a target, we discovered bicyclic macrocycles that specifically antagonize NODAL-induced signaling in cancer cells. At a 10 μM concentration, two discovered bicyclic peptides completely suppressed NODAL-induced phosphorylation of SMAD2 in P19 embryonic carcinoma cells. The TSL-[S]Y[C]KRAHKN[C] bicycle inhibited NODAL-induced proliferation of NODAL-TYK-nu ovarian carcinoma cells with apparent IC50 of 1 μM. The same bicycle at 10 μM concentration did not affect the growth of the control TYK-nu cells. TSL-bicycles remained stable over the course of the 72 hour-long assays in a serum-rich cell-culture medium. We further observed general stability in mouse serum and in a mixture of proteases (Pronase™) for 21 diverse bicyclic macrocycles of different ring sizes, amino acid sequences, and cross-linker geometries. TSL-constrained peptides to expand the previously reported repertoire of phage-displayed bicyclic architectures formed by cross-linking Cys side chains. We anticipate that it will aid the discovery of proteolytically stable bicyclic inhibitors for a variety of protein targets., A two-fold symmetric linchpin (TSL) converts readily available phage-displayed disulfide peptide libraries to proteolytically stable bicyclic peptides. The bicyclic phage library was screened to discover an antagonist of NODAL morphogen.

The Wittig reaction can be used for late stage functionalization of proteins and peptides to ligate glycans, pharmacophores, and many other functionalities. In this manuscript, we modified 160,000 N-terminal glyoxaldehyde peptides displayed on phage with the Wittig reaction by biotin labeled ylide under conditions that functionalize only 1% of the library population. Deep-sequencing of the biotinylated and input populations estimated the rate of conversion for each sequence. This “deep conversion” (DC) from deep sequencing correlates with rate constants measured by HPLC. Peptide sequences with fast and slow reactivity highlighted a critical role of primary backbone amides (N-H) in accelerating the rate of the aqueous Wittig reaction. Experimental measurement of reaction rates and density functional theory (DFT) computation of the transition state geometries corroborated this relationship. We also collected deep-sequencing data to build structure activity relationship (SAR) models that can predict DC value of the Wittig reaction. By using this data, we trained two classifier models based on Gradient Boosted trees. These classifiers achieved area under the ROC (Receiver Operating Characteristic) Curve (ROC AUC) of 81.2 ± 0.4 and 73.7 ± 0.8 (90–92% accuracy) in determining whether a sequence belonged to the top 5% or the bottom 5% in terms of its reactivity. We have deployed our learned models as a publicly available web app: http://44.226.164.95/ We anticipate that phage-displayed peptides and related mRNA or DNA-displayed substrates can be employed in a similar fashion to study the substrate scope and mechanisms of many other chemical reactions.

In this manuscript, we developed a Two-fold Symmetric Linchpin (TSL) that converts readily available phage display peptides libraries made of 20 common amino acids to genetically-encoded libraries of bicyclic peptides displayed on phage. TSL combines an aldehyde-reactive group and two thiol-reactive groups; it bridges two side chains of cysteine [C] with an N-terminal aldehyde group derived from the N-terminal serine [S], yielding a novel bicyclic topology that lacks a free N-terminus. Phage display libraries of SX1CX2X3X4X5X6X7C sequences, where Xi is any amino acids but Cys, were converted to a library of bicyclic TSL-[S]X1[C]X2X3X4X5X6X7[C] peptides in 45 ± 15% yield. Using this library and protein morphogen NODAL as a target, we discovered bicyclic macrocycles that specifically antagonize NODAL-induced signaling in cancer cells. At a 10 µM concentration, two discovered bicyclic peptides completely suppressed NODAL-induced phosphorylation of SMAD2 in P19 embryonic carcinoma. The TSL-[S]Y[C]KRAHKN[C] bicycle inhibited NODAL-induced proliferation of NODAL-Tky-nu ovarian carcinoma cells with apparent IC50 1 µM. The same bicycle at 10 µM concentration did not affect the growth of the control Tky-nu cells. TSL-bicycles remained stable over the course of the 72 hour-long assays in a serum-rich cell-culture medium. We further observed general stability in mouse serum and in a mixture of proteases (PronaseTM) for 33 diverse bicyclic macrocycles of different ring sizes, amino acid sequences, and cross-linker geometries. TSL-constrained peptides expand the previously reported repertoire of phage display bicyclic architectures formed by cross-linking Cys side chains. We anticipate that it will aid the discovery of proteolytically stable bicyclic inhibitors for a variety of protein targets.

10.1039/c3sc51124c A new titanium-based sulfide clusterfullerene, Ti2S@D3h(24109)-C78, has been successfully synthesized by arc-discharging graphite rods packed with pure TiO2 and graphite powder under an atmosphere of SO2 and helium. Multistage HPLC methods were utilized to isolate and purify the Ti2S@C78, and mass spectrometric characterization confirmed the composition of a Ti2S cluster within a C78 cage. UV-Vis-NIR absorption spectroscopy, electrochemical characterization and extensive DFT calculations led to the assignment of the cage symmetry to D3h(24109)-C78 and suggested an almost linear arrangement of the internal Ti2S cluster, with a formal transfer of six electrons from the cluster to the C78 cage.

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