Synthesis and Reactivity of 2‑(Carboxymethyl)Aziridine Derivatives
Total Page:16
File Type:pdf, Size:1020Kb
Review pubs.acs.org/CR Synthesis and Reactivity of 2‑(Carboxymethyl)aziridine Derivatives † Gert Callebaut, Tamara Meiresonne, Norbert De Kimpe,* and Sven Mangelinckx* Department of Sustainable Organic Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium 2.6.2. Multicomponent Reactions (Method VIb) 7984 2.7. Miscellaneous 7987 3. Reactivity of 2-(Carboxymethyl)aziridines 7989 3.1. Functional Group Transformations 7991 3.2. Ring Expansion to Five-Membered Rings 7992 3.2.1. Lactones 7992 3.2.2. Lactams 7996 3.2.3. Pyrrolines 7998 3.3. Ring Expansions to Six- and Seven-Mem- bered Rings 7999 3.3.1. Naphthalenes 7999 3.3.2. Pyridines and Piperidines 7999 3.3.3. Pyrimidines and Hexahydropyrimidines 8000 CONTENTS 3.3.4. Diazepines 8000 3.4. Ring Opening of 2-(Carboxymethyl)- 1. Introduction 7954 aziridines 8000 2. Synthesis of 2-(Carboxymethyl)aziridine Deriva- 3.4.1. Oxygen Nucleophiles 8000 tives 7956 3.4.2. Nitrogen Nucleophiles 8005 2.1. Synthesis Through N1−C2 Bond Formation 7958 3.4.3. Sulfur Nucleophiles 8007 2.1.1. Synthesis via Intramolecular Nucleo- 3.4.4. Carbon Nucleophiles 8008 philic Substitution (Method Ia) 7958 3.4.5. Other 8008 2.1.2. Synthesis via Rearrangement of 4- 3.5. Neighboring Group Effects 8010 Isoxazoline-5-carboxylate Derivatives 4. Conclusions and Perspectives 8010 (Method Ib) 7958 Author Information 8010 2.2. Synthesis through N1−C3 Bond Formation Corresponding Authors 8010 (Method II) 7962 Funding 8010 2.2.1. Enantioselective Synthesis Starting from Notes 8010 the Chiral Pool 7962 Biographies 8010 2.2.2. Stereoselective Synthesis Starting from Acknowledgments 8011 Addition Reactions Across Imines 7967 Abbreviations 8011 2.2.3. Synthesis from 1,2-Diaminoalkenes 7971 References 8012 2.3. Synthesis through C2−C4 Bond Formation 7971 2.3.1. Synthesis through Reaction of a 2- Aziridinyl Anion (Method IIIa) 7971 2.3.2. Synthesis Starting from 2H-Azirines 1. INTRODUCTION (Method IIIb) 7972 More than a decade ago, the question was raised by Sweeney if 2.4. Synthesis via Addition Reactions to Imines aziridines are epoxides’ ugly cousins?1 The overview on the (Method IV) 7977 biological properties, synthetic accessibility, and useful 2.4.1. Synthesis through Reaction with Car- reactivity of aziridines presented therein, and in numerous − benes 7977 earlier and later reviews,2 11 clearly indicated that this question 2.4.2. Synthesis through Reaction with Sulfur is purely rhetorical. 2-(Aziridinyl)acetic acid 1, alternatively Ylides 7979 named 3,4-iminobutanoic acid or 2-(carboxymethyl)aziridine, is 2.5. Synthesis through Reactions of Nitrene a simple β,γ-aziridino carboxylic acid, which, to the best of our fi Equivalents with Ole ns (Method V) 7979 knowledge and somewhat surprisingly, has never been reported 2.5.1. Synthesis through Addition of Azides (Figure 1). Nevertheless, this aziridine 1 can be considered as − Across Alkenes 7979 the higher homologue of aziridine-2-carboxylic acid 2,12 14 2.5.2. Synthesis via in-Situ-Generated Nitrenes 7981 2.5.3. Miscellaneous Synthesis 7983 2.6. Functional Group Transformations 7984 Special Issue: 2014 Small Heterocycles in Synthesis 2.6.1. Enantioselective Synthesis Starting from Received: October 16, 2013 the Chiral Pool (Method VIa) 7984 Published: April 28, 2014 © 2014 American Chemical Society 7954 dx.doi.org/10.1021/cr400582d | Chem. Rev. 2014, 114, 7954−8015 Chemical Reviews Review Figure 1. 2-(Aziridinyl)acetic acid 1, aziridine-2-carboxylic acid 2, β,γ-epoxy carboxylic acid 3, γ-amino-β-hydroxybutyric acid 4, and carnitine 5. which represents a very interesting electrophilic scaffold for the Although the “poly(carboxymethylethylene imine)” poly- − 26−28 29 design of cysteine protease inhibitors.15 17 Furthermore, mer and 2-aziridineacetic acid containing polypeptides aziridine 1 is the aza analog of β,γ-epoxy carboxylic acid 3, have been mentioned a few times in the literature, the synthesis of the unprotected 2-(aziridinyl)acetic acid 1 monomer has which is a valuable building block for ring opening to γ-amino- β 18 19 -hydroxybutyric acid (GABOB) 4, and carnitine 5. Scheme 1 never been reported so far. This could be due to the fact that this 2-(aziridinyl)acetic acid, 1, is likely to be unstable because it might be prone to rearrange to constitutional isomers such as Figure 2. Azinomycin A 6 and azinomycin B 7. 3-aminomethyl-β-propiolactone, 10 or, more likely, 3-amino-γ- butyrolactone, 11 (Scheme 1). Moreover, the challenging (stereoselective) synthesis of 2- β γ This , -epoxy carboxylic acid moiety is also present in (carboxymethyl)aziridines 12 (Y ≠ H) is hampered by the azinomycin A, 6, and azinomycin B, 7, in which the epoxide presence of an acidic proton in the α-position, which can easily moiety acts as an electrophile which can easily react with biological nucleophiles (Figure 2). Hereby, azinomycin A and B Scheme 2 are behaving as very efficient DNA interstrand cross-linkers as it contains, next to the epoxide moiety, also an electrophilic bicyclic aziridine unit which can react with DNA.20 As − azaheterocyclic β-amino acid derivatives,21 24 the group of 2- (carboxymethyl)aziridine derivatives 8 covers a specific part of the chemical space which is of interest for development of bioactive products and for further synthetic application toward be deprotonated, leading to ring opening with formation of the corresponding γ-amino-α,β-unsaturated carboxylic acid deriva- tives 13 (Scheme 2). Also, possible deprotonation and reprotonation at the acidic α-center must be considered as this would lead to epimerization of the chiral center. Although 2-(carboxymethyl)aziridine derivatives 8 have not yet received a lot of attention as biologically relevant compounds, some of them are exhibiting interesting biological Figure 3. 2-(Carboxymethyl)aziridine derivatives 8 and 3-(carbox- β α activities. For example, 2-aziridinyl-2-hydroxy- -lactam 14a ymethyl)- -lactam derivatives 9. showed promising ACAT inhibitor activity (using Lovastatin as a reference standard) in an in vitro assay (Figure 4).30 a wide range of nitrogen-containing compounds such as β- and Furthermore, the four enantiomers of 15a (“2-benzyl-3,4- γ-amino acids,25 amino alcohols, and heterocycles. iminobutanoic acid”) were evaluated as a novel class of The scope of the current review is not limited in time, as it is inhibitors of CPA. All four stereoisomers of 15a were found to the first dedicated report concerning the chemistry of 2- have competitive inhibitory activity against CPA, although their (carboxymethyl)aziridine derivatives 8 (Figure 3). Herein, the inhibitory potencies differ widely, (2R,3R)-15a being the most synthesis and reactivity of 2-(aziridinyl)acetic esters (X = OR), potent.31 (1R,6R)- and (1S,6S)-3,4,5-Trihydroxy-7-azabicyclo- 2-(aziridinyl)acetamides (X = NRR′), and 2-(aziridinyl)acetic [4.1.0]heptane-2-carboxylic acids 16 were evaluated as thioesters (X = SR) is discussed, without covering 2- glycosidase inhibitors because they were expected to be (aziridinyl)acetaldehydes (X = H) and the corresponding chemotherapeutic agents and biological tools for clarifying ketones (X = alkyl, aryl), as these compounds have a significant catalytic mechanisms of glycosidases. The glycosidase inhibitor distinct reactivity and applications. Also, synthesis of the 3- assay showed that both isomers of 16 are potent inhibitors of β- α ′ 32 (carboxymethyl)- -lactam derivatives 9 (X = OR, NRR , SR) glucuronidase as they had excellent IC50 values in this assay. will not be discussed for the same reason. The 2-(carboxymethyl)aziridine unit is also present in peptide- 7955 dx.doi.org/10.1021/cr400582d | Chem. Rev. 2014, 114, 7954−8015 Chemical Reviews Review Figure 4. 2-Aziridinyl-2-hydroxy-β-lactam 14a, 2-(2-aziridinyl)-3-phenylpropanoic acid 15a, 3,4,5-trihydroxy-7-azabicyclo[4.1.0]heptane-2-carboxylic acid 16, and peptide-based macrocycles 17. based macrocycles 17, which are of considerable biological 2. SYNTHESIS OF 2-(CARBOXYMETHYL)AZIRIDINE interest as their topology allows them to resist digestion by DERIVATIVES exopeptidases while retaining high affinities for their bio- − In the following section, synthesis of 2-(carboxymethyl)- chemical targets.33 43 aziridine derivatives will be dealt with. Several synthetic Moreover, the 2-(carboxymethyl)aziridine radical 18 is proposed as one of three stabilized radical intermediates approaches toward 2-(carboxymethyl)aziridines based on the different bond connections or transformations are schematically illustrated in Scheme 3. A distinction has been made between three types of intramolecular reactions (methods Ia, Ib, and II), four types of intermolecular reactions (methods IIIa, IIIb, IV, and V), and a functional group transformation (method VI). In addition, a group of miscellaneous reactions toward the synthesis of 2-(carboxymethyl)aziridines will be described. Furthermore, intramolecular reactions and addition reactions are subdivided with respect to the mechanism of these Figure 5. Stabilized 2-(carboxymethyl)aziridine radical 18. reactions. The intramolecular nucleophilic substitution reac- tions (methods Ia and II) involve attack of a nucleophilic amino group of compounds 19 and 21 on an adjacent carbon atom bearing a leaving group (LG) to afford 2-(carboxymethyl)- which inhibits the enzyme activity of ornithine 4,5-amino- aziridines. To allow aziridine synthesis in an asymmetric way, mutase (OAM) (Figure 5). Biosynthesis of this radical 18 use of starting materials derived from the chiral pool was also occurs via reaction of 2,4-diaminobutyric acid (DAB) with described (method II). Besides, an intramolecular (thermal) holo-OAM.44 rearrangement of 4-isoxazoline-5-carboxylates 20 (Y = O) has Scheme 3 7956 dx.doi.org/10.1021/cr400582d | Chem. Rev. 2014, 114, 7954−8015 Chemical Reviews Review Scheme 4 Scheme 5 Scheme 6 Scheme 7 synthetic pathway toward the corresponding 2- (carboxymethyl)aziridines (method IIIa). Furthermore, addi- tion reactions of α-deprotonated acetate derivatives 25 across 2H-azirines 24 have been performed as well via Reformatsky, Ivanov, and cycloaddition reactions (method IIIb).