Chiral tricyclic iminolactone derived from (1R)-(+)-camphor as a glycine equivalent for the asymmetric synthesis of alpha-amino acids

Copper-Catalyzed Three-Component Carboiminolactonization of Electron-Deficient Olefins

Herein we report the three-component copper-catalyzed carboiminolactonization of α,β-unsaturated carbonyl derivatives. In the presence of a Cu(I) catalyst, α-haloesters, electron-deficient alkenes, and primary amines couple to generate γ-iminolactones in a single step. The scope of the reaction is explored with respect to the three coupling partners. Nineteen examples are presented with yields of these hydrolytically labile heterocycles of up to 69%. Mechanistic investigations support the formation of an oxocarbenium by way of an atom transfer radical addition (ATRA) intermediate.

Syntheses of Cannabinoid Metabolites: Ajulemic Acid and HU-210

Cannabinoid metabolites have been reported to be more potent than their parent compounds. Among them, ajulemic acid (AJA) is a side-chain analog of Δ9-THC-11-oic acid, which would be a good template structure for the discovery of more potent analogues. Herein, we optimized the key allylic oxidation step to introduce the C-11 hydroxy group with a high yield. A series of compounds was prepared with this condition applied including HU-210, 11-nor-Δ8-tetrahydrocannabinol (THC)-carboxylic acid and Δ9-THC-carboxylic acid.

Identification of a Female-Produced Sex Attractant Pheromone of the Winter Firefly, Photinus corruscus Linnaeus (Coleoptera: Lampyridae)

Firefly flashes are well-known visual signals used by these insects to find, identify, and choose mates. However, many firefly species have lost the ability to produce light as adults. These "unlighted" species generally lack developed adult light organs, are diurnal rather than nocturnal, and are believed to use volatile pheromones acting over a distance to locate mates. While cuticular hydrocarbons, which may function in mate recognition at close range, have been examined for a handful of the over 2000 extant firefly species, no volatile pheromone has ever been identified. In this study, using coupled gas chromatography - electroantennographic detection, we detected a single female-emitted compound that elicited antennal responses from wild-caught male winter fireflies, Photinus corruscus. The compound was identified as (1S)-exo-3-hydroxycamphor (hydroxycamphor). In field trials at two sites across the species' eastern North American range, large numbers of male P. corruscus were attracted to synthesized hydroxycamphor, verifying its function as a volatile sex attractant pheromone. Males spent more time in contact with lures treated with synthesized hydroxycamphor than those treated with solvent only in laboratory two-choice assays. Further, using single sensillum recordings, we characterized a pheromone-sensitive odorant receptor neuron in a specific olfactory sensillum on male P. corruscus antennae and demonstrated its sensitivity to hydroxycamphor. Thus, this study has identified the first volatile pheromone and its corresponding sensory neuron for any firefly species, and provides a tool for monitoring P. corruscus populations for conservation and further inquiry into the chemical and cellular bases for sexual communication among fireflies.

Iminolactones from Schizophyllum commune

Schizines A (1) and B (2), the first naturally occurring iminolactones (3,6-dihydro-2H-1,4-oxazin-2-one derivatives) to be reported, have been isolated from the fruiting bodies of Schizophyllym commune. In principle the 2-oxazinone moiety might have been formed by a reaction between the amino acid phenylalanine or tryptophan and an 2α-hydroxy-1-ketomarasmone. The alkaloids are unusual in that the carboxyl group of the amino acid precursor is preserved during the biosynthesis. The compounds showed some inhibition of the growth of cancer cells.

3,3-Dimethyl-1,2,3,4-tetra-hydro-cyclo-penta-[b]indole-1,2-dione (bruceolline E)

The title compound, C(13)H(11)NO(2), crystallizes with two mol-ecules in the asymmetric unit. The crystal packing is stabilized by N-H⋯O hydrogen bonds, which link the mol-ecules into chains along [10[Formula: see text]], and weak C-H⋯O inter-actions.

Synthesis of α-amino acids based on chiral tricycloiminolactone derived from natural (+)-camphor

Amino acids are one of the most important classes of the building blocks of life: they are the structural subunits of proteins, peptides, and many secondary metabolites. In addition to the 20 α-amino acids that constitute the backbone of proteins, hundreds of other natural α-amino acids have been discovered either in free form or as components in natural products. The difference between these molecules is the substituents at the chiral carbon situated between the amino and carboxyl moieties; this carbon (and any atom along a chain attached to it) is thus an important synthetic target. Because tailor-made α-amino acids are increasingly popular in biochemistry and organic synthesis, further refinement in synthetic methods to generate both natural (L-configuration) and unnatural (D-configuration) amino acids is a very active area of current research. In this Account, we examine the tricycloiminolactones, which are versatile glycine equivalents derived from natural camphor. We have developed the tricycloiminolactones in our laboratory and used them in the synthesis of several kinds of enantiopure α-amino acids. As nucleophiles, enolated tricycloiminolactones were shown to successfully participate in alkylations, Aldol reactions, Michael additions, and Mannich reactions. These reactions all gave excellent stereoselectivities and high yields. Simple conversion of the products offered α-alkyl-α-amino acids, α,α-dialkyl-α-amino acids, β-hydroxy-α-amino acids, α,γ-diamino acids, and α,β-diamino acids. One particular advantage is that the same electrophile can react with two chiral templates in the same way, thus affording access to both enantiomeric amino acids. In other words, some natural (L-configuration) α-amino acids and their unnatural (D-configuration) counterparts can be prepared very conveniently. The relation between substrate structures and product stereoconformations derived from our investigations serves as a convenient guide in the synthesis of useful chiral amino acids. In addition, highly stereoselective 1,3-diploar cycloadditions between alkenes and chiral nitrones derived from tricycloiminolactones provide a potential method for the synthesis of γ-hydroxy-α-amino acids. We also discuss applications of our methods in the synthesis of complex natural products, including conagenin, polyoxamic acid, lactacystin, and sphingofungin F. The preparation of some clinically important drug molecules, such as thiaphenicol, florfenicol, and chloramphenicol, was greatly simplified with our methods. The tricycloiminolactones offer a number of advantages in the synthesis of both natural and unnatural α-amino acids and provide many useful building blocks in the synthetic pursuit of complex molecules.

Recent approaches towards the asymmetric synthesis of α,α-disubstituted α-amino acids

The class of alpha,alpha-disubstituted alpha-amino acids has gained considerable attention in the past decades and continues doing so. The ongoing interest in biological and chemical properties of the substance class has inspired the development of many new methodologies for their asymmetric construction, which have not found their way into the general focus of organic chemistry yet. The aim of this review is to provide an overview of the developments in the field since 1998.

Asymmetric Synthesis of α,α-Disubstituted α-Amino Acids by Diastereoselective Alkylation of Camphor-Based Tricyclic Iminolactone

A novel and convenient route for the preparation of chiral tricyclic iminolactones 9 and 10 from camphorquinone has been developed. Alkylation of iminolactones 9 and 10 provided iminolactones 16 and 17 in high yields which were, in turn, alkylated again to afford the alpha,alpha-disubstituted products in good yields (70-90%) and excellent diastereoselectivities (>98%). Hydrolysis of the alkylated iminolactones furnished the desired alpha,alpha-disubstituted alpha-amino acids in good yields and high enantiomeric excesses with good recovery yields of the chiral auxiliary 12 and 13. The extremely high endo-face selectivity for alkylation is discussed using semiempirical (MOPAC 93) calculations.

Synthetic applications of aliphatic unsaturated α-H-α-amino acids

This article provides an overview of the literature concerning synthetic applications of unsaturated aliphatic amino acids in the period May 2000 to December 2004.

Selective synthesis of either enantiomer of alpha-amino acids by switching the regiochemistry of the tricyclic iminolactones prepared from a single chiral source

Preparation of l-alpha-amino acids was easily accomplished simply by exchanging the position of the lactone group of our recently reported chiral template 1 from C2 to C3. The new chiral template 7 was prepared in 54% overall yield over five steps from (1R)-(+)-camphor. Alkylation of iminolactone 7 afforded the alpha-monosubstituted products in good yields and excellent diastereoselectivities (>98%). Hydrolysis of the alkylated iminolactones furnished the desired l-alpha-amino acids in good yields and ee with nearly quantitative recovery of chiral auxiliary 4.