[This corrects the article on p. 100 in vol. 41.].

Energy conservation in chemotrophic anaerobic bacteria.

The human diet contains a great variety of natural mutagens and carcinogens, as well as many natural antimutagens and anticarcinogens. Many of these mutagens and carcinogens may act through the generation of oxygen radicals. Oxygen radicals may also play a major role as endogenous initiators of degenerative processes, such as DNA damage and mutation (and promotion), that may be related to cancer, heart disease, and aging. Dietary intake of natural antioxidants could be an important aspect of the body’s defense mechanism against these agents. Many antioxidants are being identified as anticarcinogens. Characterizing and optimizing such defense systems may be an important part of a strategy of minimizing cancer and other age-related diseases.

https://science.sciencemag.org/content/sci/221/4617/1256.full.pdf

Dietary carcinogens and anticarcinogens Oxygen radicals and degenerative diseases

III. Foldamer Research 3910 A. Overview 3910 B. Motivation 3910 C. Methods 3910 D. General Scope 3912 IV. Peptidomimetic Foldamers 3912 A. The R-Peptide Family 3913 1. Peptoids 3913 2. N,N-Linked Oligoureas 3914 3. Oligopyrrolinones 3915 4. Oxazolidin-2-ones 3916 5. Azatides and Azapeptides 3916 B. The â-Peptide Family 3917 1. â-Peptide Foldamers 3917 2. R-Aminoxy Acids 3937 3. Sulfur-Containing â-Peptide Analogues 3937 4. Hydrazino Peptides 3938 C. The γ-Peptide Family 3938 1. γ-Peptide Foldamers 3938 2. Other Members of the γ-Peptide Family 3941 D. The δ-Peptide Family 3941 1. Alkene-Based δ-Amino Acids 3941 2. Carbopeptoids 3941 V. Single-Stranded Abiotic Foldamers 3944 A. Overview 3944 B. Backbones Utilizing Bipyridine Segments 3944 1. Pyridine−Pyrimidines 3944 2. Pyridine−Pyrimidines with Hydrazal Linkers 3945

A field guide to foldamers.

Since the discovery of organic azides by Peter Griess more than 140 years ago, numerous syntheses of these energy-rich molecules have been developed. In more recent times in particular, completely new perspectives have been developed for their use in peptide chemistry, combinatorial chemistry, and heterocyclic synthesis. Organic azides have assumed an important position at the interface between chemistry, biology, medicine, and materials science. In this Review, the fundamental characteristics of azide chemistry and current developments are presented. The focus will be placed on cycloadditions (Huisgen reaction), aza ylide chemistry, and the synthesis of heterocycles. Further reactions such as the aza-Wittig reaction, the Sundberg rearrangement, the Staudinger ligation, the Boyer and Boyer-Aube rearrangements, the Curtius rearrangement, the Schmidt rearrangement, and the Hemetsberger rearrangement bear witness to the versatility of modern azide chemistry.

Organic Azides: An Exploding Diversity of a Unique Class of Compounds

The design and implementation of cascade reactions is a challenging facet of organic chemistry, yet one that can impart striking novelty, elegance, and efficiency to synthetic strategies. The application of cascade reactions to natural products synthesis represents a particularly demanding task, but the results can be both stunning and instructive. This Review highlights selected examples of cascade reactions in total synthesis, with particular emphasis on recent applications therein. The examples discussed herein illustrate the power of these processes in the construction of complex molecules and underscore their future potential in chemical synthesis.

Cascade reactions in total synthesis.

New synthetic routes to a variety of N-heterocyclic quinones and hydroquinones are described. These include thermolyses of 4-hydroxy-4-[4-N-(benzenesulfonyl)-4-aza-1,6-dialkynyl]cyclobutenones to piperidinoquinones and 4-hydroxy-4-[3-(N-phenylamino)-1-propynyl]cyclobutenones to dihydrophenanthridinediols. Included in the array of products available by this method are benzophenanthridines, indolophenanthridines, isoindoloindoles, and pyrrolophenanthridines. The methodology was employed in a five-step synthesis of the alkaloid assoanine starting with dimethyl squarate and indoline. The key step in all of these transformations is the ring expansion of appropriately substituted 4-hydroxy-4-alkynylcyclobutenones. These are envisaged to undergo electrocyclic ring opening to the corresponding enynylketenes which ring close to diradical intermediates that then lead to products via either radical additions to proximal alkyne moieties or undergo homolytic aromatic substitution to appropriately placed aryl groups. T...

Ring Expansion of 4-Alkynylcyclobutenones. Synthesis of Piperidinoquinones, Highly Substituted Dihydrophenanthridines, Benzophenanthridines, and the Naturally Occurring Pyrrolophenanthridine, Assoanine.

Several new differentially substituted cyclobutenediones 4a-e have been prepared. Their thermal rearrangement to substituted naphthofuranones 5a-d is reported. This rearrangement involves an unprecedented intramolecular cyclization of a reactive bisketene 6, and forms the naphthofuranone system in good yield.

Harold W. Moore

Papers

Ring Expansion of 4-Alkynylcyclobutenones. Synthesis of Piperidinoquinones, Highly Substituted Dihydrophenanthridines, Benzophenanthridines, and the Naturally Occurring Pyrrolophenanthridine, Assoanine.

Generation and Intramolecular Cyclization of (2-Ethenylphenyl)bisketenes. Synthesis of Benzofuranones.

An unusual synthetic route to mesoionic pyrimidines

Cyanoketenes. cycloadditions of tert‐butylcyano‐ and chlorocyanoketene to sulfur diimides

Rearrangements of quinones