Synthesis of D-abrines by palladium-catalyzed reaction of ortho-iodoanilines with N-Boc-N-methylalanyl-substituted acetaldehyde and acetylene

The silica mineralisation properties of synthetic Silaffin-1A1 (synSil-1A1)

The synthetic monodisperse pentadecapeptide synSil-1A₁ is a representative of the microdisperse mixture of the native silaffin natSil-1A₁ produced by the diatom Cylindrotheca fusiformis. The octaphosphorylated zwitterionic synSil-1A₁ is able to mineralise silica under slightly acidic conditions at pH 5.5, which is the physiologically relevant pH range assumed. Like the posttranslational modifications of the native silaffins, synSil-1A₁ is functionalised on all four lysine and phosphorylated on all seven serine residues. We describe the synthesis of a trimethyl-δ-hydroxy-L-lysine building block, the incorporation of this choline-type amino acid in peptide synthesis and its phosphorylation, together with all further posttranslational modifications observed in the native silaffins. Quantitative structure-activity relationships from silicification experiments at high dilution reveal the unique mineralisation properties of the hyperphosphorylated peptide as a single substance and in interaction with long-chain polyamines (LCPA). Diffusion-ordered spectroscopy (DOSY) experiments reveal the formation of polyelectrolyte complexes (PEC) between synSil-1A₁ and long-chain polyamines, which promotes the silicification process. The microdroplets have an overall balanced ratio of 100-150 cationic and the same number of anionic charges. The unique zwitterionic synSil-1A₁ confirms the prevailing molecular model of biosilicification and validates it with quantitative data based on a single phosphopeptide species, avoiding the usual unphysiologically high concentrations of phosphate of many previous in vitro silicification experiments.

Synthesis of Indoles via Intermolecular and Intramolecular Cyclization by Using Palladium-Based Catalysts

As part of natural products or biologically active compounds, the synthesis of nitrogen-containing heterocycles is becoming incredibly valuable. Palladium is a transition metal that is widely utilized as a catalyst to facilitate carbon-carbon and carbon-heteroatom coupling; it is used in the synthesis of various heterocycles. This review includes the twelve years of successful indole synthesis using various palladium catalysts to establish carbon-carbon or carbon-nitrogen coupling, as well as the conditions that have been optimized.

Recent advances in the synthesis of indoles from alkynes and nitrogen sources

This review highlights ten years of success in the synthesis of indoles using alkynes and nitrogen sources as substrates.

Synthesis of C 3-symmetric star-shaped molecules containing α-amino acids and dipeptides via Negishi coupling as a key step

We demonstrate a new synthetic strategy toward star-shaped C₃-symmetric molecules containing α-amino acid (AAA) derivatives and dipeptides. In this regard, trimerization and Negishi cross-coupling reactions are used as the key steps starting from readily available 4’-iodoacetophenone and L-serine. These C₃-symmetric molecules containing AAA moieties are useful to design new ligands suitable for asymmetric synthesis and peptide dendrimers.

Formation of Non-Natural α,α-Disubstituted Amino Esters via Catalytic Michael Addition

The enolate monoanion of amino esters is explored, and the first catalytic Michael addition of α-amino esters is demonstrated. These studies indicate that the acidity of the αC-H is the primary factor determining reactivity. Thus, polyfluorophenylglycine amino esters yield novel α-amino esters in the presence of a catalytic amount of a guanidine-derived base and Michael acceptors. Reactivity requires an acidic N-H, which is accomplished using common protecting groups such as N-Bz, N-Boc, and N-Cbz. Calculations and labeling experiments provide insight into the governing principles in which a key C-to-N proton transfer occurs, resulting in an expansion of the scope to include a number of natural amino esters. The study culminates with a late-stage functionalization of peptidic γ-secretase inhibitor, DAPT.

Conformation-Enabled Total Syntheses of Ohmyungsamycins A and B and Structural Revision of Ohmyungsamycin B

The first total syntheses of the bioactive cyclodepsipeptides ohmyungsamycin A and B are described. Key features of our synthesis include the concise preparation of a linear cyclization precursor that consists of N-methyl amides and non-proteinogenic amino acids, and its macrolactamization from a bent conformation. The proposed structure of ohmyungsamycin B was revised based on its synthesis. The cyclic core of the ohmyungsamycins was shown to be responsible for the excellent antituberculosis activity, and ohmyungsamycin variants with truncated chains were evaluated for their biological activity.

Asymmetric Total Synthesis of Nannocystin A

Nannocystin A is a novel 21-membered macrolactone isolated from myxobacterium Nanocystis sp. It is a potent elongation factor 1 inhibitor and inhibits cancer cell line growth at nanomolar concentrations. In this work, a concise asymmetric total synthesis of nannocystin A has been developed, which features Sharpless epoxidation, Stille coupling, and final macrolactamization.

A Mild and General Larock Indolization Protocol for the Preparation of Unnatural Tryptophans

A mild and general protocol for the Pd(0)-catalyzed heteroannulation of o-bromoanilines and alkynes is described. Application of a Pd(0)/P((t)Bu)3 catalyst system enables the efficient coupling of o-bromoanilines at 60 °C, mitigating deleterious side reactions and enabling access to a broad range of useful unnatural tryptophans. The utility of this new protocol is demonstrated in the highly convergent total synthesis of the bisindole natural product (-)-aspergilazine A.