University:
Eastern Kentucky University
Course:
CHE 361 | Organic Chemistry I
Academic year:

2020
Views:

407

Pages:

1
Author:

Kaiden Murphy

Organic Chemistry 10: Nitrogen- and Phosphorus-Containing Compound Amino Acids, Peptides, and Proteins Amino Acid: The a-carbon of an amino acid is attached to four groups: an amino group, a carboxyl group, a hydrogen atom, and an R group. It is chiral in all amino acids except glycine. All amino acids in eukaryotes are L-amino acids. They all have (S) stereochemistry except cysteine, which is (R). Amphoteric: Amino acids are amphoteric, meaning they can act as acids or bases. Amino acids get their acidic characteristics from carboxylic acids and their basic characteristics from amino groups. In neutral solution, amino acids tend to exist as zwitterions (dipolar ions). Aliphatic: Non-aromatic. Side chain contains only C and H. Gly, Ala, Val, Leu, Ile, Pro. Met can also be considered aliphatic. Peptide Bonds: Form by condensation reactions and can be cleaved hydrolytically. Resonance of peptide bonds restricts motion about the C-N bond, which takes on partial double bond character. A strong acid or base is needed to cleave a peptide bond. Formed when the N-terminus of an AA nucleophilically attacks the C-terminus of another AA. Phosphorus-Containing Compounds Phosphoric Acid: Sometimes referred to as a phosphate group or inorganic phosphate, denoted Pi. At physiological pH, inorganic phosphate includes molecules of both hydrogen phosphate (HPO42-) and dihydrogen phosphate (H2PO4-). Phosphoric Acid Contains 3 hydrogens, each with a unique pKa. The Structure: wide variety in pKa values allows phosphoric acid to act as a buffer over a large range of pH values. Phosphodiester Phosphorus is found in the backbone of DNA, which Bonds: uses phosphodiester bonds. In forming these bonds, a pyrophosphate (PPi, P2O74-) is released. Pyrophosphate can then be hydrolyzed to two inorganic phosphates. Phosphate bonds are high energy because of large negative charges in adjacent phosphate groups and resonance stabilization of phosphates. Organic Carbon containing compounds that also have phosphate Phosphates: groups. The most notable examples are nucleotide triphosphates (such as ATP or GTP) and DNA. Polypeptides: Made up of multiple amino acids linked by peptide bonds. Proteins are large, folded, functional polypeptides. Synthesis o -Amino Acids Biologically, amino acids are synthesized in many ways. In the lab, certain standardized mechanisms are used. Strecker Generates an amino acid from an aldehyde. An Synthesis: aldeyhyde is mixed with ammonium chloride (NH4Cl) and potassium cyanide. The ammonia attacks the carbonyl carbon, generating an imine. The imine is then attacked by the cyanide, generating an aminonitrile. The aminonitrile is hydrolyzed by two equivalents of water, generating an amino acid. Gabriel Synthesis: Generates an amino acid from potassium phthalimide, diethyl bromomalonate, and an alkyl halide. Phthalimide attacks the diethyl bromomalonate, generating a phthalimidomalonic ester. The phthalimidomalonic ester attacks an alkyl halide, adding an alkyl group to the ester. The product is hydrolyzed, creating phthalic acid (with two carboxyl groups) and converting the esters into carboxylic acids. One carboxylic acid of the resulting 1,3-dicarbonyl is removed by decarboxylation. Gabriel Synthesis of an Amino Acid Strecker Synthesis of an Amino Acid