We report a sensitive LC (liquid chromatography)/MS/MS assay using selected reaction monitoring to quantify RA (retinoic acid), which is applicable to biological samples of limited size (10-20 mg of tissue wet weight), requires no sample derivatization, provides mass identification and resolves atRA (all-trans-RA) from its geometric isomers. The assay quantifies over a linear range of 20 fmol to 10 pmol, and has a 10 fmol limit of detection at a signal/noise ratio of 3. Coefficients of variation are: instrumental, 0.5-2.9%; intra-assay, 5.4+/-0.4%; inter-assay 8.9+/-1.0%. An internal standard (all-trans-4,4-dimethyl-RA) improves accuracy by confirming extraction efficiency and revealing handling-induced isomerization. Tissues of 2-4-month-old C57BL/6 male mice had atRA concentrations of 7-9.6 pmol/g and serum atRA of 1.9+/-0.6 pmol/ml (+/-S.E.M.). Tissue 13-cis-RA ranged from 2.9 to 4.2 pmol/g, and serum 13-cis-RA was 1.2+/-0.3 pmol/ml. CRBP (cellular retinol-binding protein)-null mouse liver had atRA approximately 30% lower than wild-type (P<0.05), but kidney, testis, brain and serum atRA were similar to wild-type. atRA in brain areas of 12-month-old female C57BL/6 mice were (+/-S.E.M.): whole brain, 5.4+/-0.4 pmol/g; cerebellum, 10.7+/-0.3 pmol/g; cortex, 2.6+/-0.4 pmol/g; hippocampus, 8.4+/-1.2 pmol/g; striatum, 15.3+/-4.7 pmol/g. These data provide the first analytically robust quantification of atRA in animal brain and in CRBP-null mice. Direct measurements of endogenous RA should have a substantial impact on investigating target tissues of RA, mechanisms of RA action, and the relationship between RA and chronic disease.

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Quantification of endogenous retinoic acid in limited biological samples by LC/MS/MS

Retinoid-like activity is exhibited by compounds of formula (I) where X is S, O, or NR' where R' is hydrogen or lower alkyl; R is hydrogen or lower alkyl; A is pyridyl, thienyl, furyl, pyridazinyl, pyrimidinyl or pyrazinyl; n is 0-4; and B is H, -COOH or a pharmaceutically acceptable salt, ester or amide thereof, -CH2OH or an ether or ester derivative, or -CHO or an acetal derivative, or -COR1 or a ketal derivative where R1 is -(CH2)mCH3 where m is 0-4, or a pharmaceutically acceptable salt thereof.

Disubstituted acetylenes bearing heteroaromatic and heterobicyclic groups having retinoid-like activity

Various effects of photoaging or sundamage of skin including impairment of differentiation of epidermal epithelial cells and loss of collagen fibers, abnormal changes in elastic fibers and deterioration of small blood vessels in the dermis of the skin are retarded by applying topically to the epidermis in a maintenance therapy program effective amounts of retinoids including retinoid derivatives and stereoisomers thereof such that epithelial growths are substantially reduced and prevented and the skin substantially regains and maintains its firmness, turgor and elasticity. Moreover, with persistent treatment dermal blood cells and vessels increase and the epidermis and dermis thicken, resulting in improved ability of the skin to sense, resist and recover from irritation or injury. Further, hyperpigmentation, lines and wrinkles due to aging are reduced and prevented. The treatment is particularly useful for human facial skin and preferably applied in amounts insufficient to cause excessive irritation.

Methods for treatment of sundamaged human skin with retinoids

Aryl-substituted and aryl and (3-oxo-1-propenly)-substituted benzopyran, benzothiopyran, 1,2-dihydroquinoline, and 5,6-dihydronaphthalene derivatives have retinoid negative hormone and/or antagonist-like biological activities. The invented RAR antagonists can be administered to mammals, including humans, for the purpose of preventing or diminishing action of RAR agonists on the bound receptor sites. Specifically, the RAR agonists are administered or coadministered with retinoid drugs to prevent or ameliorate toxicity or side effects caused by retinoids or vitamin A or vitamin A precursors. The retinoid negative hormones can be used to potentiate the activities of other retinoids and nuclear receptor agonists. For example, the retinoid negative hormone called AGN 193109 effectively increased the effectiveness of other retinoids and steroid hormones in in vitro transactivation assays. Additionally, transactivation assays can be used to identify compounds having negative hormone activity. These assays are based on the ability of negative hormones to down-regulate the activity of chimeric retinoid receptors engineered to possess a constitutive transcription activator domain.

Synthesis and use of retinoid compounds having negative hormone and/or antagonist activities

Reductive amination is an important tool for synthetic organic chemists in the construction of carbon-nitrogen bonds. This reaction, also termed reductive alkylation, involves condensation of an aldehyde or ketone with an amine in the presence of a reducing agent. A wide variety of substrates can be used including aliphatic and aromatic aldehydes and ketones, and even benzophenones. A range of amines from ammonia to aromatic amines, including those with electron-withdrawing substituents, can be employed. For particularly sluggish reactions, such as those involving weakly electrophilic carbonyl groups, poorly nucleophilic amines, or sterically congested reactive centers, additives such as molecular sieves or Lewis acids are often useful.



This chapter focuses on those conditions in which the carbonyl component, amine, and reducing reagent react in the same vessel. This review is restricted to reductive aminations using borohydride and borane reducing agents. This chapter concentrates on reductive amination chemistry mediated by borohydride and other boron-containing reducing agents from 1971, the year when sodium cyanoborohydride was introduced, through the middle of 1999. In addition to reductive aminations of aldehyde and ketone substrates, reactions of related structures including acetals, aminals, ketals, carboxylic acids, nitriles, and dicarbonyls that form a nitrogen-containing ring are reviewed. Intramolecular processes in which the substrate contains both the carbonyl and amine moieties are described. The intramolecular variant is a useful method for preparing cyclic amines. All of the various boron-containing hydride sources in reductive aminations, including labeled metal hydrides, are reviewed. Instances of reductive aminations that failed are described. Applications of this method to a solid support in parallel synthesis in combinatorial chemistry as well as reductive aminations that proceed in tandem with a second reaction such as reductive lactamizations are discussed.


Keywords:

organic reaction(s);
organic synthesis;
reaction(s);
synthesis;
reductive amination;
condensation;
alkylation;
reductive alkylation;
reduction;
amination;
carbonyl;
amine;
reducing agent(s);
borohydride;
borane;
carbon-nitrogen bond(s);
CN bond(s)

Reductive Aminations of Carbonyl Compounds with Borohydride and Borane Reducing Agents

Compounds of the formulas (I), (II) and (III), where R1, R2, R3 and R4 are hydrogen or methyl, X is hydrogen or fluorine and Q is formula (IV), (V), (VI), (VII), (VIII), or (IX), and X1 is hydrogen, hydroxy, methoxy or fluorine, R is hydroxy, alkoxy with 0 or 1 hydroxy substituent, aroxy or NR5R6, where R5 is hydrogen, alkyl with 0 or 1 hydroxy substituent or aryl, and R6 is alkyl with 0 or 1 hydroxy substituent or aryl, with the provisos that X is fluorine only when R2 is methyl, when R3 or R4 is methyl the other R3 or R4 is also methyl and when Q is said thienyl group Q may be in either the cis or trans position. These compounds are useful as chemopreventive agents for inhibiting tumor promotion in epithelial cells and for treating nonmalignant skin disorders.

Benzonorbornenyl, benzopyranyl and benzothiopyranyl retinoic acid analogues

A series of conformationally restricted retinoids was synthesized and screened in two assays used to measure the ability of retinoids to control cell differentiation, namely, the reversal of keratinization in tracheal organ culture from vitamin A deficient hamsters and the inhibition of the induction of mouse epidermal ornithine decarboxylase by a tumor promoter. These compounds had bonds corresponding to selected bonds of the E-tetraene chain of retinoic acid (1) held in a planar cisoid conformation by inclusion in an aromatic ring. The meta-substituted analogue 3 of 4-[(E)-2-methyl-4-(2,6,6-trimethylcyclohexenyl)-1,3-butadienyl+ ++]benzoic acid (2) was far less active than 2 in both assays. In contrast, the vinyl homologue of 2 (4) and the 7,8-dihydro and 7,8-methano analogues (5 and 6) had activity comparable to that of 2. Analogues of 4-[(E)-2-(1,1,4,4-tetramethyl-1,2,3,4-tetrahydro-6-naphthyl)propenyl] benzoic acid (7) were also screened. Replacement of the tetrahydronaphthalene ring of 7 by a benzonorbornenyl group (9) significantly reduced activity, as did removal of the vinylic methyl group from 9 (10). Replacement of the propenyl group of 9 by a cyclopropane ring (12) also reduced activity. Replacement of the tetrahydronaphthalene ring of 7 by 4,4-dimethyl-3,4-dihydro-2H-1-benzopyran and -benzothiopyran rings (13 and 14) also decreased activity. Inclusion of the 7,9 double bond system of 1 in an aromatic ring (15 and 16) reduced activity, whereas inclusion of the 5,7 double bond system in an aromatic ring enhanced activity (7 and 19). Inclusion of the 11,13 and 9,11,13 double bond systems in aromatic rings (2 and 18) also reduced activity below that of 1. Retinoic acid, 7, 13, 14, and 19 inhibited papilloma tumor formation in mice. Toxicity testing indicated that 7 was more toxic than 1, 13, 14, and 19, 19 was more toxic than 1, and 13 and 14 were less toxic than 1.

Conformationally restricted retinoids.

6-[(E)-2-(2,6,6-Trimethyl-1-cyclohexen-1-yl)ethen-1-yl]- and 6-(1,2,3,4-tetrahydro-1,1,4,4-tetramethyl-6-naphthyl)-2-naphthalenecarboxylic acids (4 and 8) have been synthesized and show significant activity in reversing the keratinization process in hamster tracheal organ culture and in inhibiting the induction of ornithine decarboxylase in mouse skin by 12-O-tetradecanoylphorbol-13-acetate, two assays used to measure retinoid activity. The 2-naphthalenecarboxylic acid 8 was more active than 4.

Synthesis and pharmacological activity of 6-[(E)-2-(2,6,6-trimethyl-1-cyclohexen-1-yl)ethen-1-yl]- and 6-(1,2,3,4-tetrahydro-1,1,4,4-tetramethyl-6-naphthyl)-2-naphthalenecarboxylic acids.

Analogues of retinoic acid that have their major modifications in the 5,6 double bond and 4-methylene group regions of the beta-cyclogeranylidene ring have been synthesized as potential agents for the treatment and prevention of epithelial cancer. These modifications were intended to reduce retinoid toxicity by lowering the effective treatment dose because the major metabolic deactivation pathway would be inhibited. Ethyl (E)-3,7-dimethyl-9-(exo-2-bicyclo[2.2.1]-heptyl)-2,4,6,8-nonatetraenoate (7), ethyl (E)-3,7-dimethyl-9-(2,2,6-trimethylbicyclo[4.1.0]hept-1-yl)-2,4,6,8-nonatetraen oate (18), (E)-1-(4-carbethoxyphenyl)-2-methyl-4-(2,2,6-trimethylbicyclo[4.1.0]hept-1-yl)- 1,3-butadiene (28), (E)-retinoic acid-4,4,18,18,18-d5 (39), and ethyl (E)-3,7-dimethyl-9-(3,3-ethano-2,6,6-trimethyl-1-cyclohexen-1-yl)-2,4,6,8-nonatetraenoate (47) displayed moderate to excellent activity in an assay for the inhibition of tumor promoter-induced mouse epidermal ornithine decarboxylase.

Retinoic acid analogues with ring modifications. Synthesis and pharmacological activity.

Aromatic analogues of (all-E)- and 13(Z)-retinoic acids have been synthesized as potential chemopreventive agents for the treatment of epithelial cancer. In the E series, (1E,3E)-1-(4-carboxyphenyl)-2-methyl-4-(2,6,6-trimethyl-1-cyclohexen-1-yl)-1,3- butadiene (7a), its ethyl ester 5a, and the epoxy ethyl ester 14 displayed excellent activity in the assay for the inhibition of tumor promotor-induced mouse epidermal ornithine decarboxylase, while (1E,3E)-1-(4-carboethoxy-3-methylphenyl)-2-methyl-4-(2,6,6-trimethyl-1-cyclohexen-1-yl)-1,3-butadiene (5b) was inactive. The 13(Z) analogues, (E)-1-(2-carboxyphenyl)-4-methyl-6-(2,6,6-trimethyl-1-cyclohexen-1-yl)-1,3,5-he xatriene (19) and (E)-1-(2-hydroxyphenyl)-4-methyl-6-(2,6,6-trimethyl-1-cyclohexen-1-yl)-1,3,5-he xatriene (27), had minimal activity.

Rebecca L. S. Chan

Papers

Benzonorbornenyl, benzopyranyl and benzothiopyranyl retinoic acid analogues

Conformationally restricted retinoids.

Synthesis and pharmacological activity of 6-[(E)-2-(2,6,6-trimethyl-1-cyclohexen-1-yl)ethen-1-yl]- and 6-(1,2,3,4-tetrahydro-1,1,4,4-tetramethyl-6-naphthyl)-2-naphthalenecarboxylic acids.

Retinoic acid analogues with ring modifications. Synthesis and pharmacological activity.

Aromatic retinoic acid analogues. Synthesis and pharmacological activity.