Thiazole

Thiazole, or 1,3-thiazole, is a 5-membered heterocyclic compound that contains both sulfur and nitrogen. The term 'thiazole' also refers to a large family of derivatives. Thiazole itself is a pale yellow liquid with a pyridine-like odor and the molecular formula C3H3NS.[2] The thiazole ring is notable as a component of the vitamin thiamine (B1).

Thiazole
Full structural formula
Skeletal formula with numbers
Ball-and-stick model
Space-filling model
Names
Preferred IUPAC name
1,3-Thiazole
Other names
Thiazole
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.005.475
UNII
  • InChI=1S/C3H3NS/c1-2-5-3-4-1/h1-3H checkY
    Key: FZWLAAWBMGSTSO-UHFFFAOYSA-N checkY
  • InChI=1/C3H3NS/c1-2-5-3-4-1/h1-3H
    Key: FZWLAAWBMGSTSO-UHFFFAOYAI
  • n1ccsc1
Properties
C3H3NS
Molar mass 85.12 g·mol−1
Boiling point 116 to 118 °C (241 to 244 °F; 389 to 391 K)
Acidity (pKa) 2.5 (of conjugate acid) [1]
-50.55·10−6 cm3/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)
Infobox references

Molecular and electronic structure

Thiazoles are members of the azoles, heterocycles that include imidazoles and oxazoles. Thiazole can also be considered a functional group when part of a larger molecule.

Thiazole rings are planar and aromatic. Thiazoles are characterized by larger pi-electron delocalization than the corresponding oxazoles and have therefore greater aromaticity. This aromaticity is evidenced by the chemical shift of the ring protons in proton NMR spectroscopy (between 7.27 and 8.77 ppm), clearly indicating a strong diamagnetic ring current. The calculated pi-electron density marks C5 as the primary site for electrophilic substitution, and C2 as the site for nucleophilic substitution.

Thiazole electron densities and numbering scheme
Thiazole electron densities and numbering scheme

Occurrence of thiazoles and thiazolium salts
Bleomycin is a thiazole-containing anti-cancer drug.

Thiazoles are found in a variety of specialized products, often fused with benzene derivatives, the so-called benzothiazoles. In addition to vitamin B1, the thiazole ring is found in epothilone. Other important thiazole derivatives are benzothiazoles, for example, the firefly chemical luciferin. Whereas thiazoles are well represented in biomolecules, oxazoles are not. It is found in naturally occurring peptides, and utilised in the development of peptidomimetics (i.e. molecules that mimic the function and structure of peptides).[3]

Commercial significant thiazoles include mainly dyes and fungicides. Thifluzamide, Tricyclazole, and Thiabendazole are marketed for control of various agricultural pests. Another widely used thiazole derivative is the non-steroidal anti-inflammatory drug Meloxicam. The following anthroquinone dyes contain benzothiazole subunits: Algol Yellow 8 (CAS# [6451-12-3]), Algol Yellow GC (CAS# [129-09-9]), Indanthren Rubine B (CAS# [6371-49-9]), Indanthren Blue CLG (CAS# [6371-50-2], and Indanthren Blue CLB (CAS#[6492-78-0]). These thiazole dye are used for dyeing cotton.

Organic synthesis

Various laboratory methods exist for the organic synthesis of thiazoles. Prominent is the Hantzsch thiazole synthesis, which is a reaction between haloketones and thioamides. For example, 2,4-dimethylthiazole is synthesized from thioacetamide and chloroacetone.[4][5] Another example [6] is given below:

Hantsch Thiazole Synthesis
Hantsch Thiazole Synthesis

Biosynthesis

Thiazoles are generally formed via reactions of cysteine, which provides the N-C-C-S backbone of the ring. Thiamine does not fit this pattern however. Several biosynthesis routes lead to the thiazole ring as required for the formation of thiamine.[7] Sulfur of the thiazole is derived from cysteine. In anaerobic bacteria, the CN group is derived from dehydroglycine.

Reactions

With a pKa of 2.5 for the conjugate acid, thiazoles are far less basic than imidazole (pKa =7).[8]

Deprotonation at C2: the negative charge on this position is stabilized as an ylide; Hauser bases and organolithium compounds react at this site, replacing the proton

Thiazole deprotonation

2-(trimethylsilyl)thiazole [9] (with a trimethylsilyl group in the 2-position) is a stable substitute and reacts with a range of electrophiles such as aldehydes, acyl halides, and ketenes
Thiazole bromination
Thiazole bromination
Thiazole Nucleophilic Aromatic Substitution
Thiazole Nucleophilic Aromatic Substitution
  • Organic oxidation at nitrogen gives the aromatic thiazole N-oxide; many oxidizing agents exist, such as mCPBA; a novel one is hypofluorous acid prepared from fluorine and water in acetonitrile; some of the oxidation takes place at sulfur, leading to non-aromatic sulfoxide/sulfone:[10] Thiazole N-oxides are useful in Palladium-catalysed C-H arylations, where the N-oxide is able to shift the reactivity to reliably favor the 2-position, and allows for these reactions to be carried out under much more mild conditions.[11]
Thiazole oxidation
Thiazole oxidation
Thiazole cycloaddition
Thiazole cycloaddition

Thiazolium salts

Alkylation of thiazoles at nitrogen forms a thiazolium cation. Thiazolium salts are catalysts in the Stetter reaction and the Benzoin condensation. Deprotonation of N-alkyl thiazolium salts give the free carbenes[12] and transition metal carbene complexes.

Structure of thiazoles (left) and thiazolium salts (right)

Alagebrium is a thiazolium-based drug.

References
  1. Zoltewicz, J. A.; Deady, L. W. (1978). Quaternization of Heteroaromatic Compounds. Quantitative Aspects. Advances in Heterocyclic Chemistry. Vol. 22. pp. 71–121. doi:10.1016/S0065-2725(08)60103-8. ISBN 9780120206223.
  2. Eicher, T.; Hauptmann, S. (2003). The Chemistry of Heterocycles: Structure, Reactions, Syntheses, and Applications. ISBN 978-3-527-30720-3.
  3. Mak, Jeffrey Y. W.; Xu, Weijun; Fairlie, David P. (2015-01-01). Peptidomimetics I (PDF). Topics in Heterocyclic Chemistry. Vol. 48. Springer Berlin Heidelberg. pp. 235–266. doi:10.1007/7081_2015_176. ISBN 978-3-319-49117-2.
  4. J. R. Byers; J. B. Dickey (1939). "2-Amino-4-methylthiazole". Organic Syntheses. 19: 10. doi:10.15227/orgsyn.019.0010.
  5. George Schwarz (1945). "2,4-Dimethylthiazole". Organic Syntheses. 25: 35. doi:10.15227/orgsyn.025.0035.
  6. Alajarín, M.; Cabrera, J.; Pastor, A.; Sánchez-Andrada, P.; Bautista, D. (2006). "On the [2+2] Cycloaddition of 2-Aminothiazoles and Dimethyl Acetylenedicarboxylate. Experimental and Computational Evidence of a Thermal Disrotatory Ring Opening of Fused Cyclobutenes". J. Org. Chem. 71 (14): 5328–5339. doi:10.1021/jo060664c. PMID 16808523.
  7. Kriek, M.; Martins, F.; Leonardi, R.; Fairhurst, S. A.; Lowe, D. J.; Roach, P. L. (2007). "Thiazole Synthase from Escherichia coli: An Investigation of the Substrates and Purified Proteins Required for Activity in vitro" (PDF). J. Biol. Chem. 282 (24): 17413–17423. doi:10.1074/jbc.M700782200. PMID 17403671.
  8. Thomas L. Gilchrist "Heterocyclic Chemistry" 3rd ed. Addison Wesley: Essex, England, 1997. 414 pp. ISBN 0-582-27843-0.
  9. Dondoni, A.; Merino, P. (1995). "Diastereoselective Homologation of D-(R)-Glyceraldehyde Acetonide using 2-(Trimethylsilyl)thiazole". Organic Syntheses. 72: 21.; Collective Volume, vol. 9, p. 952
  10. Amir, E.; Rozen, S. (2006). "Easy Access to the Family of Thiazole N-oxides using HOF·CH3CN". Chemical Communications. 2006 (21): 2262–2264. doi:10.1039/b602594c. PMID 16718323.
  11. Campeau, Louis-Charles; Bertrand-Laperle, Mégan; Leclerc, Jean-Philippe; Villemure, Elisia; Gorelsky, Serge; Fagnou, Keith (2008-03-01). "C2, C5, and C4 Azole N -Oxide Direct Arylation Including Room-Temperature Reactions". Journal of the American Chemical Society. 130 (11): 3276–3277. doi:10.1021/ja7107068. ISSN 0002-7863.
  12. Arduengo, A. J.; Goerlich, J. R.; Marshall, W. J. (1997). "A Stable Thiazol-2-ylidene and Its Dimer". Liebigs Annalen. 1997 (2): 365–374. doi:10.1002/jlac.199719970213.
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.