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310 KiB

Open AccessArticle

The Tandem Ring Opening/Ring Closing Metathesis Route to Oxaspirocycles: An Approach to Phelligridin G

by Harold D. Cooper and Dennis L. Wright

Molecules 2013, 18(2), 2438-2448; https://doi.org/10.3390/molecules18022438 - 21 Feb 2013

Cited by 11 | Viewed by 6397

Abstract

Phelligridin G is an unusual natural product that contains an embedded spiro-fused furanone core. We have investigated two furan-based synthetic approaches towards the spirocyclic core structure of this natural product from readily available 2-phenylfurans. Although initial studies involving an oxidative cyclization were unsuccessful, [...] Read more.

Phelligridin G is an unusual natural product that contains an embedded spiro-fused furanone core. We have investigated two furan-based synthetic approaches towards the spirocyclic core structure of this natural product from readily available 2-phenylfurans. Although initial studies involving an oxidative cyclization were unsuccessful, we were ultimately able to access this key system through a sequential intermolecular furan Diels-Alder reaction followed by a metathesis-based reorganization. A related approach led to an expanded C ring to form spiro-fused pyran spirocycles. Full article

(This article belongs to the Special Issue Spiro Compounds)

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315 KiB

Open AccessArticle

Synthesis of 5α-Androstane-17-spiro-δ-lactones with a 3-Keto, 3-Hydroxy, 3-Spirocarbamate or 3-Spiromorpholinone as Inhibitors of 17β-Hydroxysteroid Dehydrogenases

by Guy Bertrand Djigoué, Béatrice Tchédam Ngatcha, Jenny Roy and Donald Poirier

Molecules 2013, 18(1), 914-933; https://doi.org/10.3390/molecules18010914 - 11 Jan 2013

Cited by 10 | Viewed by 6313

Abstract

We synthesized two series of androstane derivatives as inhibitors of type 3 and type 5 17β-hydroxysteroid dehydrogenases (17β-HSDs). In the first series, four monospiro derivatives at position C17 were prepared from androsterone (ADT) or epi-ADT. After the protection of the alcohol at [...] Read more.

We synthesized two series of androstane derivatives as inhibitors of type 3 and type 5 17β-hydroxysteroid dehydrogenases (17β-HSDs). In the first series, four monospiro derivatives at position C17 were prepared from androsterone (ADT) or epi-ADT. After the protection of the alcohol at C3, the C17-ketone was alkylated with the lithium acetylide of tetrahydro-2-(but-3-ynyl)-2-H-pyran, the triple bond was hydrogenated, the protecting groups hydrolysed and the alcohols oxidized to give the corresponding 3-keto-17-spiro-lactone derivative. The other three compounds were generated from this keto-lactone by reducing the ketone at C3, or by introducing one or two methyl groups. In the second series, two dispiro derivatives at C3 and C17 were prepared from epi-ADT. After introducing a spiro-δ-lactone at C17 and an oxirane at C3, an aminolysis of the oxirane with L-isoleucine methyl ester provided an amino alcohol, which was treated with triphosgene or sodium methylate to afford a carbamate- or a morpholinone-androstane derivative, respectively. These steroid derivatives inhibited 17β-HSD3 (14–88% at 1 μM; 46–94% at 10 μM) and 17β-HSD5 (54–73% at 0.3 μM; 91–92% at 3 μM). They did not produce any androgenic activity and did not bind steroid (androgen, estrogen, glucocorticoid and progestin) receptors, suggesting a good profile for prostate cancer therapy. Full article

(This article belongs to the Special Issue Spiro Compounds)

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351 KiB

Open AccessArticle

Novel Rearrangements in the Reactions Directed Toward Preparation of Spiro-N,N-ketals: Reactions of Naphthalene-1,8-diamine with Ninhydrin and Isatin

by Motoko Akita, Hideyuki Seto, Reiko Aoyama, Junko Kimura and Keiji Kobayashi

Molecules 2012, 17(12), 13879-13890; https://doi.org/10.3390/molecules171213879 - 22 Nov 2012

Cited by 26 | Viewed by 10881

Abstract

Spiro-N,N-ketal 5, consisting of a phthaloperine heterocyclic ring and a naphtha[1,8-ef][1,4]diazepine ring, was obtained along with spiro-N,N-ketal 2 via 2,2-condensation in the reaction of ninhydrin with naphthalene-1,8-diamine. Their molecular structures were elucidated by X-ray crystal structural analysis. Aside [...] Read more.

Spiro-N,N-ketal 5, consisting of a phthaloperine heterocyclic ring and a naphtha[1,8-ef][1,4]diazepine ring, was obtained along with spiro-N,N-ketal 2 via 2,2-condensation in the reaction of ninhydrin with naphthalene-1,8-diamine. Their molecular structures were elucidated by X-ray crystal structural analysis. Aside from these spiro compounds, the diazapleiadiene compound 3 formed by 1,2-condensation and the 1,4-isoquinolinedione compound 4 arising from ring expansion were isolated. When isatin was reacted with naphthalene-1,8-diamine, spiro-N,N-ketal 6 and the two 1H-perimidine-based compounds 7 and 8 were isolated. Compound 8 was revealed to undergo a fast dynamic prototropic tautomerization in solution. Plausible mechanisms of the formation of the products are proposed. Full article

(This article belongs to the Special Issue Spiro Compounds)

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320 KiB

Open AccessArticle

Spiroheterocyclization of Methyl 1-Aryl-3-cinnamoyl-4,5-dioxo-4,5-dihydro-1H-pyrrole-2-carboxylates by the Action of 3-(Arylamino)-1H-inden-1-ones

by Pavel S. Silaichev, Valeriy O. Filimonov, Pavel A. Slepukhin and Аndrey N. Maslivets

Molecules 2012, 17(12), 13787-13794; https://doi.org/10.3390/molecules171213787 - 22 Nov 2012

Cited by 8 | Viewed by 8010

Abstract

Methyl 1-aryl-3-cinnamoyl-4,5-dioxo-4,5-dihydro-1H-pyrrole-2-carboxylates interact with 3-(arylamino)-1H-inden-1-ones to give the corresponding 1,1'-diaryl-3'-cinnamoyl-4'-hydroxy-1H-spiro[indeno[1,2-b]pyrrole-3,2'-pyrrole]-2,4,5'(1'H)-triones in good yields. Full article

(This article belongs to the Special Issue Spiro Compounds)

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373 KiB

Open AccessArticle

Mechanistic Study of the Spiroindolones: A New Class of Antimalarials

by Bin Zou, Peiling Yap, Louis-Sebastian Sonntag, Seh Yong Leong, Bryan K. S. Yeung and Thomas H. Keller

Molecules 2012, 17(9), 10131-10141; https://doi.org/10.3390/molecules170910131 - 24 Aug 2012

Cited by 34 | Viewed by 6931

Abstract

During the synthesis of the new antimalarial drug candidate NITD609, a high degree of diastereoselectivity was observed in the Pictet-Spengler reaction. By isolating both the 4E and 4Z imine intermediates, a systematic mechanistic study of the reaction under both kinetic and [...] Read more.

During the synthesis of the new antimalarial drug candidate NITD609, a high degree of diastereoselectivity was observed in the Pictet-Spengler reaction. By isolating both the 4E and 4Z imine intermediates, a systematic mechanistic study of the reaction under both kinetic and thermodynamic conditions was conducted. This study provides insight into the source of the diastereoselectivity for this important class of compounds. Full article

(This article belongs to the Special Issue Spiro Compounds)

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366 KiB

Open AccessArticle

Synthesis and Structure of New 3,3,9,9-Tetrasubstituted-2,4,8,10-Tetraoxaspiro[5.5]undecane Derivatives

by Alin Mihiş, Eric Condamine, Elena Bogdan, Anamaria Terec, Tibor Kurtán and Ion Grosu

Molecules 2008, 13(11), 2848-2858; https://doi.org/10.3390/molecules13112848 - 17 Nov 2008

Cited by 14 | Viewed by 10391

Abstract

The configurational and conformational behavior of some new 3,3,9,9-tetrasubstituted-2,4,8,10-tetraoxaspiro[5.5]undecane derivatives with axial chirality was investigated by conformational analysis and variable temperature NMR experiments. Full article

(This article belongs to the Special Issue Spiro Compounds)

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194 KiB

Open AccessArticle

Antibacterial Properties of 3 H-Spiro[1-benzofuran-2,1’-cyclohexane] Derivatives from Heliotropium filifolium

by Alejandro Urzúa, Javier Echeverría, Marcos C. Rezende and Marcela Wilkens

Molecules 2008, 13(10), 2385-2393; https://doi.org/10.3390/molecules13102385 - 1 Oct 2008

Cited by 40 | Viewed by 10642

Abstract

A re-examination of cuticular components of Heliotropium filifolium allowed the isolation of four new compounds: 3’-hydroxy-2’,2’,6’-trimethyl-3H-spiro[1-benzo-furan-2,1’-cyclohexane]-5-carboxylic acid(2), methyl 3’-acetyloxy-2’,2’,6’-trimethyl-3H-spiro[1-benzofuran-2,1’-cyclohexane]-5-carboxylate (3), methyl 3’-isopentanoyloxy-2’,2’,6’-trimethyl-3H-spiro[1-benzofuran-2,1’-cyclohexane]-5-carboxylate (4) and methyl 3’-benzoyloxy-2’,2’,6’-trimethyl-3H-spiro[1-benzofuran-2,1’-cyclohexane]-5-carboxylate (5).Compounds 2-5 were identified by their spectroscopic analogies with [...] Read more.

A re-examination of cuticular components of Heliotropium filifolium allowed the isolation of four new compounds: 3’-hydroxy-2’,2’,6’-trimethyl-3H-spiro[1-benzo-furan-2,1’-cyclohexane]-5-carboxylic acid(2), methyl 3’-acetyloxy-2’,2’,6’-trimethyl-3H-spiro[1-benzofuran-2,1’-cyclohexane]-5-carboxylate (3), methyl 3’-isopentanoyloxy-2’,2’,6’-trimethyl-3H-spiro[1-benzofuran-2,1’-cyclohexane]-5-carboxylate (4) and methyl 3’-benzoyloxy-2’,2’,6’-trimethyl-3H-spiro[1-benzofuran-2,1’-cyclohexane]-5-carboxylate (5).Compounds 2-5 were identified by their spectroscopic analogies with filifolinol (1), and their structures confirmed by chemical correlation with 1. The antimicrobial properties of the compounds were tested against Gram positive and Gram negative bacteria. Some of them proved to be active against Gram positive, but inactive against Gram negative bacteria. In searching for structure-activity relationships from the obtained MIC values, lipophilicity was shown to be an important variable. Full article

(This article belongs to the Special Issue Spiro Compounds)

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203 KiB

Open AccessArticle

Synthesis of a Novel D-Glucose-Conjugated 15-Crown-5 Ether with a Spiro Ketal Structure

by Takashi Yamanoi, Yoshiki Oda, Hitomi Muraishi and Sho Matsuda

Molecules 2008, 13(8), 1840-1845; https://doi.org/10.3390/molecules13081840 - 22 Aug 2008

Cited by 7 | Viewed by 9037

Abstract

This paper describes a synthetic approach to a novel D-glucose-conjugated 15-crown-5 ether having a spiroketal structure starting from a 1-C-vinylated glucose derivative. The approach consists of the glycosylation of the vinylated glucose derivative to give an ethyleneoxy spacer derivative using bismuth(III) triflate, the [...] Read more.

This paper describes a synthetic approach to a novel D-glucose-conjugated 15-crown-5 ether having a spiroketal structure starting from a 1-C-vinylated glucose derivative. The approach consists of the glycosylation of the vinylated glucose derivative to give an ethyleneoxy spacer derivative using bismuth(III) triflate, the conversion of the 1-C-vinyl group of the glucoside produced into a carboxylic acid group, and the intramolecular condensation between the carboxyl group and the terminal hydroxyl group in the ethyleneoxy spacer. A D-glucose-conjugated 15-crown-5 ether having a unique spiroketal structure was thus successfully synthesized. Full article

(This article belongs to the Special Issue Spiro Compounds)

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759 KiB

Open AccessArticle

1,2,5,10,11,14-Hexaoxadispiro[5.2.5.2]hexadecanes: Novel Spirofused Bis-Trioxane Peroxides

by Axel G. Griesbeck, Lars-Oliver Höinck, Johann Lex, Jörg Neudörfl, Dirk Blunk and Tamer T. El-Idreesy

Molecules 2008, 13(8), 1743-1758; https://doi.org/10.3390/molecules13081743 - 19 Aug 2008

Cited by 7 | Viewed by 10997

Abstract

A set of new bis-spirofused 1,2,4-trioxanes 4a-d was obtained from the reaction of cyclohexane-1,4-dione with allylic hydroperoxides 2a-d, bearing an additional hydroxy group in the homoallylic position, by diastereoselective photooxygenation of allylic alcohols 1a-d and subsequent BF₃-catalyzed peroxyacetalization with the diketone. [...] Read more.

A set of new bis-spirofused 1,2,4-trioxanes 4a-d was obtained from the reaction of cyclohexane-1,4-dione with allylic hydroperoxides 2a-d, bearing an additional hydroxy group in the homoallylic position, by diastereoselective photooxygenation of allylic alcohols 1a-d and subsequent BF₃-catalyzed peroxyacetalization with the diketone. From the reaction of a monoprotected cyclohexane-1,4-dione 5 with the allylic hydroperoxide 6 derived from the singlet oxygenation of methyl hydroxytiglate, one monospiro compound was obtained, the 1,2,4-trioxane ketone 7, as well as a mixture of the diastereoisomeric syn- and anti bis-1,2,4-trioxanes 8. The structures of bis-1,2,4-trioxanes were examined theoretically by DFT methods and compared with X-ray structural data in order to evaluate the preferential trioxane ring conformational orientation. Full article

(This article belongs to the Special Issue Spiro Compounds)

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178 KiB

Open AccessArticle

Density Functional Theory Study of the Trans-Trans-Cis (TTC)→Trans-Trans-Trans (TTT) Isomerization of a Photochromic Spiropyran Merocyanine

by Grazia Cottone, Rosina Noto and Gianfranco La Manna

Molecules 2008, 13(6), 1246-1252; https://doi.org/10.3390/molecules13061246 - 3 Jun 2008

Cited by 17 | Viewed by 12996

Abstract

Density Functional Theory (DFT) calculations have been performed on the TTC→TTT isomerization reaction of the open forms of the 1',3'-dihydro-8-bromo-6-nitro- 1',3',3'-trimethylspiro[2H-1-benzopyran-2,2'-(2H)indole (8-Br-6-nitro-BIPS) system. The calculations were carried out in vacuo and in methylene chloride solution at different temperatures. Results are compared with the [...] Read more.

Density Functional Theory (DFT) calculations have been performed on the TTC→TTT isomerization reaction of the open forms of the 1',3'-dihydro-8-bromo-6-nitro- 1',3',3'-trimethylspiro[2H-1-benzopyran-2,2'-(2H)indole (8-Br-6-nitro-BIPS) system. The calculations were carried out in vacuo and in methylene chloride solution at different temperatures. Results are compared with the available experimental values of free energy difference and activation energy in solution. Full article

(This article belongs to the Special Issue Spiro Compounds)

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59 KiB

Open AccessArticle

Novel Spiroannulated 3-Benzofuranones. Synthesis and Inhibition of the Human Peptidyl Prolyl cis/trans Isomerase Pin1

by Manfred Braun, Anahita Hessamian-Alinejad, Boris Féaux De Lacroix, Birte Hernandez Alvarez and Gunter Fischer

Molecules 2008, 13(4), 995-1003; https://doi.org/10.3390/molecules13040995 - 29 Apr 2008

Cited by 27 | Viewed by 11304

Abstract

The novel 3H-spiro[1-benzofuran-2-cyclopentan]-3-one skeleton has been madeaccessible by different routes. One- and two-step protocols lead to tricyclic and tetracyclicbenzofuranones 2 and 3, respectively. A four-step synthesis to spirocompound 4 isdescribed. The novel spirocyclic benzofuranones display modest to no inhibition of thehuman peptidyl prolyl [...] Read more.

The novel 3H-spiro[1-benzofuran-2-cyclopentan]-3-one skeleton has been madeaccessible by different routes. One- and two-step protocols lead to tricyclic and tetracyclicbenzofuranones 2 and 3, respectively. A four-step synthesis to spirocompound 4 isdescribed. The novel spirocyclic benzofuranones display modest to no inhibition of thehuman peptidyl prolyl cis/trans isomerase Pin1. Full article

(This article belongs to the Special Issue Spiro Compounds)

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73 KiB

Open AccessArticle

Spirowallichiione: A Rearranged Multiflorane from Euphorbia wallichii Hook F. (Euphorbiaceae)

by Muhammad Shaiq Ali, Shakeel Ahmed and Muhammad Saleem

Molecules 2008, 13(2), 405-411; https://doi.org/10.3390/molecules13020405 - 18 Feb 2008

Cited by 15 | Viewed by 9332

Abstract

Euphorbia wallichii of the family Euphorbiaceae yielded a new rearrangedpentacyclic triterpene of the multiflorane class which we have named spirowallichiione.The structure of this natural spirocompound was elucidated with the aid of modernspectroscopic techniques, including 2D-NMR. Full article

(This article belongs to the Special Issue Spiro Compounds)

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87 KiB

Open AccessArticle

A Facile Route to Diastereomeric Phosphorus Ylides. Chemoselective Synthesis of Dialkyl (E)-2-[1-(2-Oxocyclopentylidene)ethyl]-2-butenedioates

by Sakineh Asghari, Mohammad Bagher Poushani and Samaneh Ramezani

Molecules 2008, 13(2), 331-339; https://doi.org/10.3390/molecules13020331 - 7 Feb 2008

Cited by 9 | Viewed by 8866

Abstract

2-Acetylcyclopentanone undergoes a smooth reaction with triphenylphosphineand dialkyl acetylenedicarboxylates to produce dialkyl 2-(1-acetyl-2-oxocyclopentyl)-3-(1,1,1-triphenyl-λ⁵-phosphanylidene)succinates. These compounds undergo intramolecularWittig reactions in boiling benzene to produce highly strained spirocyclobutenederivatives, which spontaneously undergo ring-opening reactions to produce dialkyl (E)-2-[1-(2-oxocyclopentyliden)ethyl]-2-butenedioates. Full article

(This article belongs to the Special Issue Spiro Compounds)

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Review

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405 KiB

Open AccessReview

Recent Synthetic Approaches Toward Non-anomeric Spiroketals in Natural Products

by Sylvain Favre, Pierre Vogel and Sandrine Gerber-Lemaire

Molecules 2008, 13(10), 2570-2600; https://doi.org/10.3390/molecules13102570 - 17 Oct 2008

Cited by 61 | Viewed by 19456

Abstract

Many natural products of biological interest contain [6,5]- and [6,6]-spiroketal moieties that can adopt various configurations, benefiting or not from anomeric conformation stabilizing effects. The spiroketal fragments are often important for the biological activity of the compounds containing them. Most stable spiroketal stereoisomers, [...] Read more.

Many natural products of biological interest contain [6,5]- and [6,6]-spiroketal moieties that can adopt various configurations, benefiting or not from anomeric conformation stabilizing effects. The spiroketal fragments are often important for the biological activity of the compounds containing them. Most stable spiroketal stereoisomers, including those benefiting from conformational anomeric effects (gauche conformers can be more stable than anti conformers because of a contra-steric stabilizing effect), are obtained easily under acidic conditions that permit acetal heterolysis (formation of tertiary oxycarbenium ion intermediates). The synthesis of less stable stereoisomers requires stereoselective acetal forming reactions that do not permit their equilibration with their most stable stereoisomers or, in the case of suitably substituted derivatives, concomitant reactions generating tricyclic products that quench the less stable spiroketal conformers. Ingenuous approaches have been recently developed for the synthesis of naturally occurring [6,6]- and [5,6]-nonanomeric spiroketals and analogues. The identification of several parameters that can influence the stereochemical outcome of spirocyclization processes has led to seminal improvements in the selective preparation of the non-anomeric isomers that are discussed herein. This review also gives an up-dated view of conformational anomeric effect which represents a small fraction of the enthalpic anomeric effect that makes gem-dioxy substituted compounds much more stable that their 1,n-dioxy substituted isomers (n > 1). Although models assuming sp³-hybridized oxygen atoms have been very popular (rabbit ears for the two non-bonding electron pairs of oxygen atom), sp²-hybridized oxygen atoms are used to describe the conformational anomeric effect. Full article

(This article belongs to the Special Issue Spiro Compounds)

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486 KiB

Open AccessReview

Useful Spectrokinetic Methods for the Investigation of Photochromic and Thermo-Photochromic Spiropyrans

by Mounir Maafi

Molecules 2008, 13(9), 2260-2302; https://doi.org/10.3390/molecules13092260 - 25 Sep 2008

Cited by 31 | Viewed by 12917

Abstract

This review reports on the main results of a set of kinetic elucidation methods developed by our team over the last few years. Formalisms, procedures and examples to solve all possible AB photochromic and thermophotochromic kinetics are presented. Also, discussions of the operating [...] Read more.

This review reports on the main results of a set of kinetic elucidation methods developed by our team over the last few years. Formalisms, procedures and examples to solve all possible AB photochromic and thermophotochromic kinetics are presented. Also, discussions of the operating conditions, the continuous irradiation experiment, the spectrokinetic methods testing with numerical integration methods, and the identifiability/distinguishability problems, are included. Full article

(This article belongs to the Special Issue Spiro Compounds)

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845 KiB

Open AccessReview

Asymmetric Synthesis of Naturally Occuring Spiroketals

by B. Rama Raju and Anil K. Saikia

Molecules 2008, 13(8), 1942-2038; https://doi.org/10.3390/molecules13081942 - 28 Aug 2008

Cited by 81 | Viewed by 16102

Abstract

Spiroketals are widely found as substructures of many naturally occurring compounds from diverse sources including plants, animals as well as microbes. Naturally occurring spiroketals are biologically active and most of them are chiral molecules. This article aims at reviewing the asymmetric synthesis of [...] Read more.

Spiroketals are widely found as substructures of many naturally occurring compounds from diverse sources including plants, animals as well as microbes. Naturally occurring spiroketals are biologically active and most of them are chiral molecules. This article aims at reviewing the asymmetric synthesis of biologically active spiroketals for last 10 years (1998-2007). Full article

(This article belongs to the Special Issue Spiro Compounds)

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512 KiB

Open AccessReview

Chemical and Enzymatic Approaches to Carbohydrate-Derived Spiroketals: Di-D-Fructose Dianhydrides (DFAs)

by M. Isabel García-Moreno, Juan M. Benito, Carmen Ortiz Mellet and José M. García Fernández

Molecules 2008, 13(8), 1640-1670; https://doi.org/10.3390/molecules13081640 - 12 Aug 2008

Cited by 31 | Viewed by 16995

Abstract

Di-D-fructose dianhydrides (DFAs) comprise a unique family of stereoisomeric spiro-tricyclic disaccharides formed upon thermal and/or acidic activation of sucroseand/ or D-fructose-rich materials. The recent discovery of the presence of DFAs in food products and their remarkable nutritional features has attracted considerable interest from [...] Read more.

Di-D-fructose dianhydrides (DFAs) comprise a unique family of stereoisomeric spiro-tricyclic disaccharides formed upon thermal and/or acidic activation of sucroseand/ or D-fructose-rich materials. The recent discovery of the presence of DFAs in food products and their remarkable nutritional features has attracted considerable interest from the food industry. DFAs behave as low-caloric sweeteners and have proven to exert beneficial prebiotic nutritional functions, favouring the growth of Bifidobacterium spp. In the era of functional foods, investigation of the beneficial properties of DFAs has become an important issue. However, the complexity of the DFA mixtures formed during caramelization or roasting of carbohydrates by traditional procedures (up to 14 diastereomeric spiroketal cores) makes evaluation of their individual properties a difficult challenge. Great effort has gone into the development of efficient procedures to obtain DFAs in pure form at laboratory and industrial scale. This paper is devoted to review the recent advances in the stereoselective synthesis of DFAs by means of chemical and enzymatic approaches, their scope, limitations, and complementarities. Full article

(This article belongs to the Special Issue Spiro Compounds)

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168 KiB

Open AccessReview

Stable Spirocyclic Meisenheimer Complexes

by Rabih O. Al-Kaysi, Iluminada Gallardo and Gonzalo Guirado

Molecules 2008, 13(6), 1282-1302; https://doi.org/10.3390/molecules13061282 - 9 Jun 2008

Cited by 36 | Viewed by 19416

Abstract

Meisenheimer complexes are important intermediates in Nucleophilic Aromatic Substitution Reactions (S_NAr). They are formed by the addition of electron rich species to polynitro aromatic compounds or aromatic compounds with strong electron withdrawing groups. It is possible to distinguish two types of [...] Read more.

Meisenheimer complexes are important intermediates in Nucleophilic Aromatic Substitution Reactions (S_NAr). They are formed by the addition of electron rich species to polynitro aromatic compounds or aromatic compounds with strong electron withdrawing groups. It is possible to distinguish two types of Meisenheimer or σ-complexes, the σ^Hcomplex or σ^X-complex (also named ipso), depending on the aromatic ring position attacked by the nucleophile (a non-substituted or substituted one, respectively). Special examples of σ^X- or ipso-complexes are formed through intermediate spiro adducts, via intramolecular SNAr. Some of these spirocyclic Meisenheimer complexes, a type of σ^Xcomplex, are exceptionally stable in solution and/or as solids. They can be isolated and characterized using X-ray, and various spectroscopic techniques such as NMR, UV-Vis, IR, and fluorescence. A few of these stable spirocyclic Meisenheimer complexes are zwitterionic and exhibit interesting photophysical and redox properties. We will review recent advances, synthesis and potential applications of these stable spirocyclic Meisenheimer complexes. Full article

(This article belongs to the Special Issue Spiro Compounds)

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189 KiB

Open AccessReview

New Cleft-like Molecules and Macrocycles from Phosphonate Substituted Spirobisindanol

by Giuseppe A. Consiglio, Salvatore Failla and Paolo Finocchiaro

Molecules 2008, 13(3), 678-700; https://doi.org/10.3390/molecules13030678 - 20 Mar 2008

Cited by 4 | Viewed by 12604

Abstract

We have synthetized medium-sized cyclophanes and macrocycles containingphosphonic groups, directly linked to the aromatic rings of the phanes or as pendant arms,for use as specific receptors for the selective complexation of neutral guests or forcomplexing lanthanides, as luminescent sensors and for diagnostic bioassays [...] Read more.

We have synthetized medium-sized cyclophanes and macrocycles containingphosphonic groups, directly linked to the aromatic rings of the phanes or as pendant arms,for use as specific receptors for the selective complexation of neutral guests or forcomplexing lanthanides, as luminescent sensors and for diagnostic bioassays in medicine.Furthermore, because it would be of great interest for biochemistry as well as forpharmacological studies to dispose of preorganized rigid chiral hosts for biorelevantmolecules we designed inter alia, some new chiral macrocycles capable of a triple bindingmode and we used them for constructing macrocycles that could also be of interest forchiral recognition and chiral separations. Thus, in this paper we shall review the salientaspects of some macrocycles synthetized in our laboratory, all possessing the phosphonatemoiety and a spirobisindanol scaffold and able to act as complexing agents for cations andorganic substrates. In particular, we shall describe their NMR characterization, theirstereochemistry in solution and in the solid state, and their use as chiral receptors forbiorelevant molecules. Chiral HPLC resolution of some of them is also reported. Full article

(This article belongs to the Special Issue Spiro Compounds)

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89 KiB

Open AccessReview

Nitroalkanes as Central Reagents in the Synthesis of Spiroketals

by Roberto Ballini, Marino Petrini and Goffredo Rosini

Molecules 2008, 13(2), 319-330; https://doi.org/10.3390/molecules13020319 - 7 Feb 2008

Cited by 37 | Viewed by 13158

Abstract

Nitroalkanes can be profitably employed as carbanionic precursors for theassembly of dihydroxy ketone frameworks, suitable for the preparation of spiroketals. Thecarbon-carbon bond formation is carried out exploiting nitroaldol and Michael reactions,while the nitro to carbonyl conversion (Nef reaction) ensures the correct introduction of [...] Read more.

Nitroalkanes can be profitably employed as carbanionic precursors for theassembly of dihydroxy ketone frameworks, suitable for the preparation of spiroketals. Thecarbon-carbon bond formation is carried out exploiting nitroaldol and Michael reactions,while the nitro to carbonyl conversion (Nef reaction) ensures the correct introduction of theketo group. Several spiroketal systems endowed with considerable biological activity canbe prepared using this synthetic strategy. Full article

(This article belongs to the Special Issue Spiro Compounds)

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