Amino Aldehydes Revisited

Facile synthesis of new N-(aminocycloalkylene)amino acid compounds using chiral triflate esters with N-Boc-aminopyrrolidines and N-Boc-aminopiperidines

In this study, we prepared a series of new N-(aminocycloalkylene)amino acid derivatives for use in chiral building blocks. The method was based on the conversion of enantiopure α-hydroxy acid esters into the corresponding chiral triflate esters, which were displaced by a nucleophilic substitution SN2 reaction with aminopyrrolidine and aminopiperidine derivatives, and the inversion of the configuration to give methyl 2-[(Boc-amino)cycloamin-1-yl]alkanoates with good yield and high enantiomeric and diastereomeric purity. Synthesized 2-[(Boc-amino)piperidin-1-yl]propanoates combined with ethyl l-phenylalaninate gave new chiral N-Boc- and N-nosyl-dipeptides containing a piperidine moiety. The structures were elucidated by 1H-, 13C-, and 15N-NMR spectroscopy, high-resolution mass spectrometry, and X-ray crystallography analyses.

Prebiotic Synthesis and Isomerization in Interstellar Analog Ice: Glycinal, Acetamide, and Their Enol Tautomers

Glycinal (HCOCH₂ NH₂ ) and acetamide (CH₃ CONH₂ ) are simple molecular building blocks of biomolecules in prebiotic chemistry, though their origin on early Earth and formation in interstellar media remain a mystery. These molecules are formed with their tautomers in low temperature interstellar model ices upon interaction with simulated galactic cosmic rays. Glycinal and acetamide are accessed via barrierless radical-radical reactions of vinoxy (⋅CH₂ CHO) and acetyl (⋅C(O)CH₃ ), and then undergo keto-enol tautomerization. Exploiting tunable photoionization reflectron time-of-flight mass spectroscopy and photoionization efficiency (PIE) curves, these results demonstrate fundamental reaction pathways for the formation of complex organics through non-equilibrium ice reactions in cold molecular cloud environments. These molecules demonstrate an unconventional starting point for abiotic synthesis of organics relevant to contemporary biomolecules like polypeptides and cell membranes in deep space.

Exploring the abundance of oleate hydratases in the genus Rhodococcus-discovery of novel enzymes with complementary substrate scope

Oleate hydratases (Ohys, EC 4.2.1.53) are a class of enzymes capable of selective water addition reactions to a broad range of unsaturated fatty acids leading to the respective chiral alcohols. Much research was dedicated to improving the applications of existing Ohys as well as to the identification of undescribed Ohys with potentially novel properties. This study focuses on the latter by exploring the genus Rhodococcus for its plenitude of oleate hydratases. Three different Rhodococcus clades showed the presence of oleate hydratases whereby each clade was represented by a specific oleate hydratase family (HFam). Phylogenetic and sequence analyses revealed HFam-specific patterns amongst conserved amino acids. Oleate hydratases from two Rhodococcus strains (HFam 2 and 3) were heterologously expressed in Escherichia coli and their substrate scope investigated. Here, both enzymes showed a complementary behaviour towards sterically demanding and multiple unsaturated fatty acids. Furthermore, this study includes the characterisation of the newly discovered Rhodococcus pyridinivorans Ohy. The steady-state kinetics of R. pyridinivorans Ohy was measured using a novel coupled assay based on the alcohol dehydrogenase and NAD⁺-dependent oxidation of 10-hydroxystearic acid.