Design, synthesis, and bioactivity of the first nonsteroidal mimetics of brassinolide

Ten novel compounds, each consisting of two subunits and a linker, were designed with the aid of molecular modeling to resemble the natural steroidal phytohormone brassinolide. The mimetics were synthesized and subjected to the rice leaf lamina inclination bioassay to test for brassinosteroid activity. Most of the mimetics displayed very weak or no bioactivity, but two were strongly active when coapplied with the auxin indole-3-acetic acid (IAA), which synergizes the activity of brassinosteroids. Thus, 1-(4,6 alpha,7 alpha-trihydroxy-5,6,7,8-tetrahydronaphthyl)-2-(6 alpha',7 alpha'-dihydroxy-5',6',7',8'-tetrahydronaphthyl)ethyne (4) and (E)-1,2-bis[trans-(4a alpha,8a beta)-4-oxo-6 alpha,7 alpha-dihydroxy-4a,5,6,7,8,8a-hexahydro-(3H)-naphthyl]ethylene (11) showed exceptional activity at doses as low as 0.01 ng and 0.001 ng/plant, respectively. These compounds are the first biologically active nonsteroidal brassinolide mimetics.     

Synthesis of New Brassinosteroid 24-Norcholane Type Analogs Conjugated in C-3 with Benzoate Groups

The metabolism of brassinosteroid leads to structural modifications in the ring skeleton or the side alkyl chain. The esterification and glycosylation at C-3 are the most common metabolic pathways, and it has been suggested that conjugate brassinosteroids are less active or inactive. In this way, plants regulate the content of active brassinosteroids. In this work, the synthesis of brassinosteroid 24-norcholane type analogs conjugated at C-3 with benzoate groups, carrying electron donor and electron attractant substituents on the aromatic ring, is described. Additionally, their growth-promoting activities were evaluated using the Rice Lamina Inclination Test (RLIT) and compared with that exhibited by brassinolide (used as positive control) and non-conjugated analogs. The results indicate that at the lowest tested concentrations (10⁻⁸–10⁻⁷ M), all analogs conjugated at C-3 exhibit similar or higher activities than brassinolide, and the diasteroisomers with S configuration at C-22 are the more active ones. Increasing concentration (10⁻⁶ M) reduces the biological activities of analogs as compared to brassinolide.     

Chemical synthesis and biological evaluation of cis- and trans-12,13-cyclopropyl and 12,13-cyclobutyl epothilones and related pyridine side chain analogues

The design, chemical synthesis, and biological evaluation of a series of cyclopropyl and cyclobutyl epothilone analogues (3-12, Figure 1) are described. The synthetic strategies toward these epothilones involved a Nozaki-Hiyama-Kishi coupling to form the C15-C16 carbon-carbon bond, an aldol reaction to construct the C6-C7 carbon-carbon bond, and a Yamaguchi macrolactonization to complete the required skeletal framework. Biological studies with the synthesized compounds led to the identification of epothilone analogues 3, 4, 7, 8, 9, and 11 as potent tubulin polymerization promoters and cytotoxic agents with (12R,13S,15S)-cyclopropyl 5-methylpyridine epothilone A (11) as the most powerful compound whose potencies (e.g. IC(50) = 0.6 nM against the 1A9 ovarian carcinoma cell line) approach those of epothilone B. These investigations led to a number of important structure-activity relationships, including the conclusion that neither the epoxide nor the stereochemistry at C12 are essential, while the stereochemistry at both C13 and C15 are crucial for biological activity. These studies also confirmed the importance of both the cyclopropyl and 5-methylpyridine moieties in conferring potent and potentially clinically useful biological properties to the epothilone scaffold.     

Determination of traces of natural brassinosteroids as dansylaminophenylboronates by liquid chromatography with fluorimetric detection

A microanalytical method for the determination of traces of natural brassinosteroids as their dansylaminophenylboronates by liquid chromatography with fluorimetric detection is described. The boronates are easily prepared by the reaction of brassinosteroids with dansylaminophenylboronic acid (DABA), which was newly synthesized as a precolumn fluorogenic reagent for brassinosteroids. The potential of the method is demonstrated by the separation of a standard brassinosteroid mixture and the analysis of a biologically active fraction sample obtained from an extract of Zea mays L. pollen. The detection limit of the DABA derivative was found to be 25 pg for brassinolide, which is superior to that of the phenanthreneboronate derivative.     

Structure and bonding in a cyclobutyl tris(pyrazolyl)boratoniobium complex and the variation in agostic behaviour with ring size in the series Tp(Me2)NbCl(c-C(n)H(2n-1))(MeC[triple bond]CMe), n = 3-6

The synthesis and characterisation of the cyclobutyl complex Tp(Me2)NbCl(c-C4H7)(MeC[triple bond]CMe) completes the family of cycloalkyl complexes Tp(Me2)NbCl(c-C(n)H(2n-1)), n = 3-6. The properties of the cyclobutyl complex are qualitatively similar to those of its cyclopentyl and cyclohexyl analogues, and dramatically different from those of the cyclopropyl derivative. Most conspicuously, the cyclobutyl system has an alpha-C-H agostic interaction in the dominant isomer, with no evidence for the alpha-C-C agostic character found for the smaller ring. C-C agostic character therefore seems to be unique to the cyclopropyl complex, where the acute C-C-C angles destabilise the C-C bonding orbitals.     

Synthesis of (24R)-homobrassinolide

The synthesis from stigmasterol of C-29 brassinosteroids containing an (R)-ethyl group at C24 — (24R)-homocastasterone and (24R)-homobrassinolide — is described. The structure of the carbon skeleton of the side-chain was achieved by condensing a C-22 aldehyde with the appropriate sulfone     

25,26,27-三失碳-B-高-7-氧-6-酮-5α-胆甾-3α,24-二醇的合成

本文报道以3α-羟基-6-羰基-5α-胆烷酸甲酯(3)为原料经六步反应合成了油菜甾醇类似物25,26,27-三失碳-B-高-7-氧-6-酮-5α-胆甾-3α,24-二醇(9a).总产率14%.9a的促进植物生长作用是24-表油菜甾醇内酯的60%.     

Exploring the hydroxylation-dehydrogenation connection: novel catalytic activity of castor stearoyl-ACP Delta(9) desaturase

The novel product profile obtained by incubating chiral fluorinated substrate analogues with castor stearoyl-ACP Delta(9) desaturase has been rationalized through a series of labeling studies. It was found that the introduction of the Z-double bond between C-9 and C-10 of the parent substrate occurs with pro-R enantioselectivity--a result that accounts for the observed stereochemistry of oxidation products derived from (9R)- and (9S)-9-fluorostearoyl-ACP. Oxidation of (9R)-9-fluorostearoyl-ACP occurs via at least two rapidly interchanging substrate conformations in the active site as detected by reaction pathway branching induced by deuteration at C-10 and C-11. Hydroxylation and desaturation of this substrate share the same site of initial oxidative attack.     

Biological Activity of Brassinosteroids – Direct Comparison of Known and New Analogs in planta

A systematic investigation of structural modifications of brassinosteroids is presented. We describe in detail their synthetic preparation, which includes significant improvements of previously reported protocols as well as access to new analogs with functional modifications of the steroid skeleton and of the C(17)‐attached side chain. We report the biological potency of the prepared brassinosteroid analogs as plant hormones, which were carefully established in the French bean second internode elongation assay and discuss our observations in light of the recently reported structural data detailing the molecular interactions between brassinolide in the trimeric complex with the protein receptors kinases BRASSINOSTEROID INSENSITIVE 1 (BRI 1) and SOMATIC EMBRYOGENESIS RECEPTOR KINASE 1 (SERK 1). In a further part of this work we describe the preparation of H₂O‐soluble pro‐forms of 24‐epicastasterone and we discuss their physical properties, hydrolytic stabilities and biological activity.     

Synthesis and pharmacological evaluation of new progesterone esters as 5alpha-reductase inhibitors

In this study we report the synthesis and pharmacological evaluation of four new progesterone derivatives; 17alpha-hydroxy-16beta-methylpregna-4,6-diene-3,20-dione 12, 17alpha-cyclopropylcarbonyloxy-16beta-methylpregna-4,6-diene-3,20-dione 13, 17alpha-cyclobutylcarbonyloxy-16beta-methylpregna-4,6-diene-3,20-dione 14, 17alpha-acetoxy-16beta-methylpregna-4,6-diene-3,20-dione 15 and the pregnatriene compound 17alpha-cyclobutylcarbonyloxy-16beta-methylpregna-1,4,6-triene-3,20-dione 16. The pharmacological effect of these compounds was determined in vivo as well as in vitro. The evaluation in vivo was carried out on gonadectomized male hamsters that were injected subcutaneously daily with testosterone (T) and/or finasteride, or with the novel compounds. At the end of the treatments the animals were sacrificed and the prostates were weighed. It was observed that when testosterone (T) and finasteride or compounds 12-16 were injected together, the weight of the prostate decreased significantly as compared to that of the testosterone-treated animals. The 5alpha-reductase inhibitory activity was evaluated in vitro using human prostate homogenates. These experiments showed the following IC50 values: compound 12 (alcohol at C-17) 1.2 x 10(-6) M, 13 (cyclopropyl substituent at C-17) 7.9 x 10(-10) M, 14 (cyclobutyl substituent) 3.2 x 10(-8) M, 15 (acetoxy substituent) 6.3 x 10(-11) M and 16 (cyclobutyl substituent) 3.9 x 10(-6) M. It is evident from these data that when the size of the substituent at C-17 is decreased, the 5alpha-reductase inhibitory activity increases. Apparently, in this biological model, the 5alpha-reductase inhibitory activity depends upon the steric effect of the substituent at C-17. However, the free alcohol 12 showed much lower 5alpha-reductase inhibitory activity.     

Synthesis of (24R)-homobrassinolide

The synthesis from stigmasterol of C-29 brassinosteroids containing an (R)-ethyl group at C24 — (24R)-homocastasterone and (24R)-homobrassinolide — is described. The structure of the carbon skeleton of the side-chain was achieved by condensing a C-22 aldehyde with the appropriate sulfoneInstitute of Organic Chemistry, Belarus Academy of Sciences, Minsk. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 385–391, May–June, 1994.     

Probing the reactivity of nebularine N1-oxide. A novel approach to C-6 C-substituted purine nucleosides

A novel approach to the synthesis of purine nucleoside analogues, featuring the reaction of the C6-N1-O⁻ aldonitrone moiety of 9-ribosyl-purine (nebularine) N1-oxide with some representative dipolarophiles, as well as Grignard reagents, is reported. Addition of Grignard reagents to the electrophilic C-6 carbon of the substrate allows a facile access to C-6 C-substituted purine nucleosides without using metal catalysts. 1,3-Dipolar cycloaddition processes lead to novel nucleoside analogues via opening, degradation or ring-enlargement of the pyrimidine ring of the base system of the first-formed isoxazoline or isoxazolidine cycloadduct.     

新型植物生长激素油菜甾醇内酯的合成

本文综述了新型植物生长激素油菜甾醇内酯及其类似物的合成,并简要地讨论了它们的结构与生物活性的关系。     

Synthesis of tricyclic analogues of methyllycaconitine using ring closing metathesis to append a B ring to an AE azabicyclic fragment

The synthesis of several ABE tricyclic analogues of the alkaloid methyllycaconitine 1 is reported. The analogues contain two key pharmacophores: a homocholine motif formed from a tertiary N-ethyl amine in a 3-azabicyclo[3.3.1]nonane ring system and a 2-(3-methyl-2,5-dioxopyrrolidin-1-ly)benzoate ester 4. The synthesis of the ABE tricyclic analogues of MLA 1 began with selective allylation at C-3 of 3 to produce allyl beta-keto ester 4. Double Mannich reaction of 4 with ethylamine and formaldehyde produced bicyclic amine 5 The C-9 ketone of bicyclic amine 5 was selectively reduced to form bicyclic alcohols 6 and 7 which were subsequently allylated to form dienes 8 and 9. Ring closing metathesis of dienes 8 and 9 afforded tricyclic ethers 11 and 12, respectively, the C-8 ester of which was reduced to a hydroxymethyl group to form ABE tricyclic analogues 13 and 14. Addition of allylmagnesium bromide to the C-9 ketone of 20 afforded dienes 21 and 22, which underwent ring closing metathesis to form tricyclic esters 23 and 24, respectively. Reduction of the C-8 ethyl ester of 23 and 24 to a hydroxymethyl group afforded diols 25 and 26 respectively. The 2-(3-methyl-2,5-dioxopyrrolin-1-ly)benzoate ester was introduced by conversion of alcohols 13, 14, 25 and 26, to the anthranilate esters 16, 17, 27 and 28 using N-(trifluoroacetyl)anthranilic acid 15 followed by fusion with methylsuccinic anhydride to afford the substituted anthranilates 18, 19, 29 and 30 containing the key 2-(3-methyl-2,5-dioxopyrrolidin-1-ly)benzoate ester pharmacophore.     

Labeled brassinosteroids for biochemical studies

The present paper describes the results of our studies on the synthesis of brassinolide biosynthetic precursors as tools for investigations of new biosynthetic routes leading to brassinosteroids. The corresponding labeled compounds containing three or six deuterium atoms at terminal methyl group(s) of the side chain (in a position ensuring lack of isotopic exchange) were prepared starting from stigmasterol or bisnorcholenic acid. Two strategies for the construction of the carbon skeleton of the side chain were applied in this study: Claisen rearrangement of allylic alcohols and convergent synthesis based on the coupling of 22-aldehydes with appropriate chiral sulfone. More than 20 brassinolide precursors (actual or suspected) have been prepared for metabolic studies that enabled identification of new brassinosteroids and biosynthetic subpathways to brassinolide in Secale cereale and Arabidopsis thaliana.     

Enzymatic desaturation of fatty acids: delta11 desaturase activity on cyclopropane acid probes

The formation of methylenecyclopropanes by enzymatic desaturation of 11-cyclopropylundecanoic acid (1) and its disubstituted derivatives cis- and trans-3-5 has been investigated using the Delta(11) desaturase of Spodoptera littoralis as model enzyme. Gas chromatography coupled to mass spectrometry analyses of methanolyzed lipidic extracts from tissues incubated with each probe revealed that all the cyclopropyl fatty acids were transformed into the corresponding 11-cyclopropylidene acids, except for compound trans-5 (5b), which was not desaturated at C11. The formation of methylenecyclopropane 9 as the only reaction product from 1 indicates that a potential radical intermediate is too short-lived to allow rearrangement reactions. Information on the Delta(11) desaturase substrate binding domain is provided considering the cyclopropyl probes 3-5 as conformationally restricted analogues of the straight-chain substrates.     

STUDY ON THE SYNTHESIS OF BRASSINOLIDE AND RELATED COMPOUNDS 15.FORMAL SYNTHESIS OF BRASSINOLIDE VIA STEREOSELECTIVE SULFENATE-SULFOXIDE TRANSFORMATION

A formal synthesis of the natural growth promoting steroidbrassinolide is described,which involves construction of side chainby 1,3-sulfoxide-hydroxyl transposition with methylation from(24S)-22-E-24-sulfoxide 6 and(24R)-22-E-24-sulfoxide 9,respectively to(22S)-23-E-24-methyl compound 4.     

The Cycloalkyl Ring Effect on the Spin State of Di(Thiocyanato)Bis(N-Cycloalkyl-Substituted-2-Pyridinaldimine) Iron(II)

A new series of octahedral iron(II) complexes with the composition Fe(II) (N-R-2-pyridinaldimine)₂(NCS)₂, where R=cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl, have been synthesized and the spin states of the iron atom have been studied by means of Mössbauer spectroscopy and magnetic measurement.     

The cyclopropyl effect on the regioselectivity of coupling reactions involving the lithiation of 1-cyclopropyl-2-arylacetylenes

The cyclopropyl effect controlled the regioselectivity of the cross coupling reactions of propargylic/allenylic metallic species with electrophiles affording alkynic cyclopropanes. It was proposed that the strain in cyclopropyl ring, which makes the formation of vinylidenecyclopropanes unfavorable, determined the regioselectivity. Control experiment of i-propyl, cyclobutyl, and cyclohexyl- phenylacetylenes were conducted to support the above speculation.     

Palladium-catalyzed cross-coupling of stereospecific potassium cyclopropyl trifluoroborates with aryl bromides

[reaction: see text] Stereospecific cyclopropanation of alkenylboronic esters of pinacol followed by in situ treatment with excess KHF(2) afforded the corresponding potassium cyclopropyl trifluoroborates in high yields, which then underwent Suzuki-Miyaura cross-coupling reactions with aryl bromides to give cyclopropyl-substituted arenes in good yields with retention of configuration. This promises to be a useful method for the synthesis of enantiomerically pure cyclopropanes.