Search results for "synthesis"

Selektive enzymatische Schutzgruppenabspaltungen: Der n-Heptylester als Carboxylschutzgruppe in der Peptidsynthese

1991

Selective Enzymatic Removal of Protecting Groups: n-Heptyl Esters as Carboxy Protecting Functions in Peptide Synthesis Amino acid heptyl (Hep) esters are accessible as generally crystalline hydro tosylates 3 from the amino acids by azeotropic esterification with 1-heptanol in high yields. They can be condensed with Z-, Boc-, and Aloc-protected amino acids to give the dipeptides 7–9 in the presence of 1-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ). From the fully protected dipeptides the N-terminal protecting groups are cleaved by chemical methods without affecting the Hep esters. On the other hand, the heptyl esters can be hydrolyzed under mild conditions (pH = 7.0, 37°C) and with hi…

Conjugate Alkynylation of Electrophilic Double Bonds. From Regioselectivity to Enantioselectivity

2018

This review surveys the historical efforts addressed toward the development of the conjugate alkynylation reaction. The regio- and enantioselective conjugate alkynylation of electron-deficient double bonds, most commonly unsaturated carbonyl compounds, has been an elusive reaction for a long time. Intensive research during the last decades has resulted in the identification of a number of effective reagents and catalysts to perform this reaction. Non-stereoselective conjugate alkynylation of unsaturated carbonyl compounds was first achieved by using preformed alkynyl organometallics and later with terminal alkynes under catalytic conditions. These methods paved the way for the development o…

Synthetic Approaches to Anti-Inflammatory Macrolactones of the Oxacyclododecindione Type

2015

Various synthetic approaches to the oxacyclododecindione-type macrolactones, known for their potent anti-inflammatory activity, are presented. These include an attempted carbonylative ring closure, a hydroacylation route, and an approach by ring-closing metathesis and double bond isomerization, as well as a strategy including ring-closing metathesis/unsaturation. The last route allowed the preparation of a bioactive analogue of the recently described 14-deoxyoxacyclododecindione.

Total Synthesis of a Partial Structure from Arabinogalactan and Its Application for Allergy Prevention

2020

Abstract Arabinogalactan, a microheterogeneous polysaccharide occurring in plants, is known for its allergy‐protective activity, which could potentially be used for preventive allergy treatment. New treatment options are highly desirable, especially in a preventive manner, due to the constant rise of atopic diseases worldwide. The structural origin of the allergy‐protective activity of arabinogalactan is, however, still unclear and isolation of the polysaccharide is not feasible for pharmaceutical applications due to a variation of the activity of the natural product and contaminations with endotoxins. Therefore, a pentasaccharide partial structure was selected for total synthesis and subse…

Metabolism of Linoleic Acid or Mevalonate and 6-Pentyl-α-Pyrone Biosynthesis by Trichoderma Species

1993

The understanding of the biosynthetic pathway of 6-pentyl-α-pyrone in Trichoderma species was achieved by using labelled linoleic acid or mevalonate as a tracer. Incubation of growing cultures of Trichoderma harzianum and T. viride with [U- 14 C]linoleic acid or [5- 14 C]sodium mevalonate revealed that both fungal strains were able to incorporate these labelled compounds (50 and 15%, respectively). Most intracellular radioactivity was found in the neutral lipid fraction. At the initial time of incubation, the radioactivity from [ 14 C]linoleic acid was incorporated into 6-pentyl-α-pyrone more rapidly than that from [ 14 C]mevalonate. No radioactivity incorporation was detected in 6-pentyl-…

A very simple one-pot electrosynthesis of nitrones starting from nitro and aldehyde components

2018

The cathodic treatment of nitroarenes in the presence of aldehydes yields directly and selectively nitrones. Electrolysis can be conducted on a very simple undivided beaker-type cell under constant current conditions. The conversion tolerates multiple bonds, a variety of functional groups and heterocyclic moieties. Competing reductive conversions such as pinacolization are not observed. The green aspects of this electro-conversion are avoidance of metals, an environmentally benign solvent mixture, and stable as well as sustainable carbon electrodes.

Utilization of C14-glucose for amino acids and protein synthesis by the sea urchin embryo

1962

Enzymatic and Metabolic Studies on Isolated Nuclei

1957

Publisher Summary In protein synthesis it is important to distinguish between the net synthesis of protein, as measured by an increased amount of protein nitrogen or by the formation of proteins with specific biological properties, such as enzymatically and immunologically active proteins, and exchange reactions, which may be observed in isotope experiments and, which reflect the replacement of an amino acid in a protein molecule with one from its environment. Incorporation of an amino acid into a protein can occur only during net synthesis; both types of reaction occur in similar systems. In true synthesis of protein it is usually difficult to obtain synthesis of a specific entity, especia…

Protochlorophyllide Reduction: Mechanisms and Evolution¶

2007

Protochlorophyllide (Pchlide) reductases are key enzymes in the process of chlorophyll biosynthesis. In this review, current knowledge on the molecular organization, substrate specificity and assembly of the light-dependent reduced nicotinamide adenine dinucleotide phosphate:Pchlide oxidoreductases are discussed. Characteristics of light-independent enzymes are also described briefly, and the possible reasons for the selection of light-dependent enzymes during the course of evolution are discussed.

Carotenoids

2009

Publisher Summary This chapter provides an overview of what is known about carotenoid metabolism in Chlamydomonas with reference to other green algae and vascular plants. The biosynthesis of carotenoids and the subdivisions of carotenogenesis are described. With respect to subcellular distribution, the carotenoids in vegetative cells localize to the chloroplast where they either serve as photosynthetic pigments bound to the protein complexes of the two photosystems, or as components of the eyespot apparatus is outlined with its functional significance. Carotenoids can serve as precursors of a number of other molecules with important physiological functions in Chlamydomonas.