On the Origin of Primitive Cells: From Nutrient Intake to Elongation of Encapsulated Nucleotides

Recent major discoveries in membrane biophysics hold the key to a modern understanding of the origin of life on Earth. Membrane bilayer vesicles have been shown to provide a multifaceted microenvironment in which protometabolic reactions could have developed. Cell‐membrane‐like aggregates of amphiphilic molecules capable of retaining encapsulated oligonucleotides have been successfully created in the laboratory. Sophisticated laboratory studies on the origin of life now show that elongation of the DNA primer takes place inside fatty acid vesicles when activated nucleotide nutrients are added to the external medium. These studies demonstrate that cell‐like vesicles can be sufficiently permeable to allow for the intake of charged molecules such as activated nucleotides, which can then take part in copying templates in the protocell interior. In this Review we summarize recent experiments in this area and describe a possible scenario for the origin of primitive cells, with an emphasis on the elongation of encapsulated nucleotides.     

Photochirogenesis: photochemical models on the absolute asymmetric formation of amino acids in interstellar space

Proteins of all living organisms including plants, animals, and humans are made up of amino acid monomers that show identical stereochemical L-configuration. Hypotheses for the origin of this symmetry breaking in biomolecules include the absolute asymmetric photochemistry model by which interstellar ultraviolet (UV) circularly polarized light (CPL) induces an enantiomeric excess in chiral organic molecules in the interstellar/circumstellar media. This scenario is supported by a) the detection of amino acids in the organic residues of UV-photo-processed interstellar ice analogues, b) the occurrence of L-enantiomer-enriched amino acids in carbonaceous meteorites, and c) the observation of CPL of the same helicity over large distance scales in the massive star-forming region of Orion. These topics are of high importance in topical biophysical research and will be discussed in this review. Further evidence that amino acids and other molecules of prebiotic interest are asymmetrically formed in space comes from studies on the enantioselective photolysis of amino acids by UV-CPL. Also, experiments have been performed on the absolute asymmetric photochemical synthesis of enantiomer-enriched amino acids from mixtures of astrophysically relevant achiral precursor molecules using UV-circularly polarized photons. Both approaches are based on circular dichroic transitions of amino acids that will be highlighted here as well. These results have strong implications on our current understanding of how life's precursor molecules were possibly built and how life selected the left-handed form of proteinogenic amino acids.     

Stereospecific cyclodehydration of 1,4-sulfanylalcohols to thiolanes: mechanistic insights

A series of thiolanes were prepared by cyclodehydration of sulfanylalcohols in the presence of catalytic amounts of p-toluenesulfonic acid or by using K10 clay. The sulfur heterocycles were synthesised in good to excellent yields using either a conventional Dean-Stark method or microwave irradiation under solvent-free conditions. The reaction could be performed regio- and stereoselectively and its mechanism was investigated by means of enantio- and diastereomerically enriched substrates. In contrast to previous studies, our results are consistent with an intramolecular S_N2-type mechanism as a general pathway.     

The (+)‐cis‐ and (+)‐trans‐Olibanic Acids: Key Odorants of Frankincense

Frankincense (olibanum) is one of the oldest aromatic materials used by humans, but the key molecular constituents contributing to its characteristic odor remained unknown. Reported herein is the discovery that (1S,2S)‐(+)‐trans‐ and (1S,2R)‐(+)‐cis‐2‐octylcyclopropyl‐1‐carboxylic acids are highly potent and substantive odorants occurring in ppm amounts in all of the frankincense samples analyzed, even those showing radically different volatile compositions. These cyclopropyl‐derived acids provide the very characteristic old churchlike endnote of the frankincense odor.