Calcium diglutamate

Calcium diglutamate, sometimes abbreviated CDG and also called calcium biglutamate, is a compound with formula Ca(C₅H₈NO₄)₂. It is a calcium acid salt of glutamic acid. CDG is a flavor enhancer (E number E623)—it is the calcium analog of monosodium glutamate (MSG). Because the glutamate is the actual flavor-enhancer, CDG has the same flavor-enhancing properties as MSG but without the increased sodium content.^[1] Notably, only the L isomer is used in flavouring as D-glutamate does not have an umami/savoury flavour.^[2][3]

Calcium diglutamate

Names
IUPAC name Calcium bis[(2S)- 2-amino-4-carboxy-butyrate]
Other names Calcium biglutamate L-Glutamic acid calcium salt
Identifiers
CAS Number	anhydrous: 5996-22-5 Y tetrahydrate: 69704-19-4 Y
3D model (JSmol)	anhydrous: Interactive image
Abbreviations	CDG, CBG
Beilstein Reference	11158966
ChemSpider	anhydrous: 2766261
ECHA InfoCard	100.025.307
E number	E623 (flavour enhancer)
PubChem CID	anhydrous: 3527266 tetrahydrate: 71310219
UNII	anhydrous: 9FA5OTO85L Y tetrahydrate: IPW75840KB Y
CompTox Dashboard (EPA)	anhydrous: DTXSID00894986
InChI anhydrous: InChI=1/2C5H9NO4.Ca.2H/c2*6-3(5(9)10)1-2-4(7)8;;;/h2*3H,1-2,6H2,(H,7,8)(H,9,10);;;/p-4/t2*3-;;;/m00.../s1/r2C5H9NO4.CaH2/c2*6-3(5(9)10)1-2-4(7)8;/h2*3H,1-2,6H2,(H,7,8)(H,9,10);1H2/p-4/t2*3-;/m00./s1 Key: ZKUDDWCZGPUNQH-VDEFSOALBX
SMILES anhydrous: C(CC(=O)[O-])C(C(=O)[O-])N.C(CC(=O)[O-])C(C(=O)[O-])N.[Ca+2]
Properties
Chemical formula	C10H16CaN2O8
Molar mass	332.322 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

As a soluble source of calcium ions, this chemical is also used as a first-aid treatment for exposure to hydrofluoric acid.^[4]

Synthesis and reactions

Calcium di-glutamate can be prepared by reacting calcium carbonate with two molar equivalents of glutamic acid:^[5]

CaCO₃ + 2 HOOC(CH₂)₂CH(NH₂)COOH → Ca(OOC(CH₂)₂CH(NH₃)COO)₂ + H₂O + CO₂↑

Concentration of the solution to a syrup under reduced pressure, followed by gradual crystallisation, affords the monohydrate.^[5] Structurally, the glutamate anion is zwitterionic, with the amino group protonated (pK_a = 9.47) and both carboxylic-acid groups (pK_a = 2.10, 4.07) in their deprotonated carboxylate form.^[6]

Calcium di-L-glutamate can be used to prepare other glutamates through metathesis with a soluble sulfate, carbonate or hydroxide salt. For example, manganese(II) di-L-glutamate can be prepared through metathesis with manganese(II) sulphate:^[7]

Ca(OOC(CH₂)₂CH(NH₃)COO)₂ + MnSO₄ → Mn(OOC(CH₂)₂CH(NH₃)COO)₂ + CaSO₄↓

References

1. Ball, P.; Woodward, D.; Beard, T.; Shoobridge, A.; Ferrier, M. (Jun 2002). "Calcium diglutamate improves taste characteristics of lower-salt soup". European Journal of Clinical Nutrition (Free full text). 56 (6): 519–523. doi:10.1038/sj.ejcn.1601343. ISSN 0954-3007. PMID 12032651.
2. Kawai, Misako; Sekine-Hayakawa, Yuki; Okiyama, Atsushi; Ninomiya, Yuzo (2012). "Gustatory sensation of L- and D-amino acids in humans". Amino Acids. 43 (6): 2349–2358. doi:10.1007/s00726-012-1315-x. ISSN 0939-4451. PMID 22588481.
3. Schiffman, S; Sennewald, K; Gagnon, J (1981). "Comparison of taste qualities and thresholds of D- and L-amino acids". Physiology & Behavior. 27 (1): 51–59. doi:10.1016/0031-9384(81)90298-5. PMID 7267802.
4. "First Aid for Chemical and Cleanroom Laboratories". Archived from the original on 2009-04-30. Retrieved 2009-06-10.
5. Sakata, Yoshiki; Horikawa, Toshiyuki; Takenouchi, Kuniharu (1963). "Alkaline Earth Salts of Glutamic Acid and Optical Resolution of their Racemic Modifications". Agricultural and Biological Chemistry. 27 (7): 518–525. doi:10.1080/00021369.1963.10858140. ISSN 0002-1369.
6. Einspahr, H.; Bugg, C. E. (1979-02-15). "Calcium binding to α-amino acids: the crystal structure of calcium di-L-glutamate tetrahydrate". Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry. 35 (2): 316–321. doi:10.1107/S0567740879003435.
7. Devereux, Michael; Jackman, Maura; McCann, Malachy; Casey, Michael (1998). "Preparation and catalase-type activity of manganese(II) amino acid complexes". Polyhedron. 17 (1): 153–158. doi:10.1016/S0277-5387(97)00211-8.