4,8-Anhydro-N-acetylneuraminic acid. Isolation from edible bird's nest and structure determination

Abstract

A new, sialic-acid-derived compound was isolated from the acid hydrolysate of edible bird's nest by ionexchange chromatography. Combined use of mass spectroscopy and 'H-and 13C-NMR spectroscopy established that it is the 4,g-anhydro derivative of N-acetylneuraminic acid and that in solutions it exists in two tautomeric forms.The formation of the new compound supports and earlier finding that in the glycoprotein of edible bird's nest at least a portion of N-acetylneuraminic acid is acetylated at HO-4.Recently we needed gram quantities of N-acetyl-D-neuraminic acid (Neu5Ac) for synthetic work aimed at reconstructing Neu5Ac-containing oligosaccharides of the capsular polysaccharides of group B streptococci [l]. Neu5AcCollocalia niucoid, the nest-cementing glycopratein substance of Chinese swift, which can be obtained [2] by aqueous extraction of edible bird's nest, a Chinese delicacy, is reported [2] to contain about 9% of Neu5Ac and is, therefore, a practical source of Neu5Ac. The isolation of Neu5Ac from this glycoprotein has been the subject of several publications, using hot water extraction [3, 41, acid hydrolysis [5] and combined enzymatic and acid hydrolysis [6]. Although in our hands hot water extraction of edible bird's nest gave no practical amounts of NeuSAc, mild acid hydrolysis, followed by ionexchange chromatographic isolation, as described [5], gave Neu5Ac in yields comparable to those published [3 -51. Also obtained was a second, previously uncharacterized compound (I). In the present paper we describe the isolation and structural investigation of this new compound. MATERIALS AND METHODSEdible bird's nest was obtained from a local Chinese grocery. N-Acetyh-neuraminic acid was obtained from Pfanstiehl Laboratories, Inc. (Waukegan, IL) and was used without purification. All other chemicals were analytical grade commercial reagents. Analytical methodsThin-layer chromatography was carried out on precoated, 0.25-mm silica gel plates (Kieselgel 60 F254 of E. Merck, Darmstadt, FRG; cat. no. 5765) with propanol/water ( 3 : 1, by vol.) (solvent A) and on pre-coated, 0.1-mm cellulose plates (pre-coated TLC Sheets, cellulose of E. Merck, Darmstadt, FRG; cat. no. 5537) with propanol/butanol/O.l M HCI (2:1:1, by vol.) [6] (solvent B). Detection was made by spraying with resorcinol/Cu2 + reagent [7] followed by heating at 110°C.Colorimetric tests, using resorcinol/Cu2 +, periodic acid/ resorcinol/Cu2 + and periodic acidlthiobarbituric acid were carried out as published [7 -91 using an LKB Ultrospec 4050 spectrophotometer.Optical rotation was measured with a Perkin-Elmer 243 automatic polarimeter.Combined gas-liquid chromatography/mass spectrometry of derivatives of lwas performed on a Hewlett-Packard 5985B instrument operated in the electron impact mode at an ionization potential of 70 eV, ion-source temperature 200 "C, using a 3% OV-17-coated fused-silica capillary column (25 m x 0.3 mm) at a temperature program at 200 -260 "C at 2 "C/ min .The 'H-and 13C-NMR spectra were recorded with a Bruker AM-500 spectromet...

Chemistry, biochemistry and biology of sialic acids

“…Fragments A and B indicate the molecular mass of the sialic acid derivatives and thereby the type and the number of substituents. [63]; for EI MS data of permethylated Kdn, see ref. Fragment A is formed from the molecular ion by the elimination of a methyl group originating from a trimethylsilyl substituent in trimethylsilylated (0-acylated0-alkylated) N-acylneuraminic acid derivatives.…”

Edible bird's nest extract inhibits influenza virus infection

“…Many studies have been carried out on the tonic effects of EBN, and it has been shown that EBN stimulates mitosis hormones and the growth factor for epidermal growth, resulting in repair of cells and stimulation of the immune system (Kong et al, 1987;Ng et al, 1986). Recently, several carbohydrate molecules, including new sialic acid-containing compounds and glycoconjugates, have been detected in EBN (Pozsgay et al, 1987;Reuter et al, 1989;Wieruszeski et al, 1987;Kakehi et al, 1994;Martin et al, 1977;Yu-Qin et al, 2000), but the importance of sialic acid residues in EBN is not clear.…”

Protein glycosylation

“…They differ not only in the substituent on the amino group (acetyl or glycoloyl), but also in the number (up to three), position (4, 7, 8 and 9) and nature (acetyl, lactoyl and methyl) of substituents on the hydroxyl groups of neuraminic acid. A recent addition is 4,6-anhydro-N-acetylneuraminic, acid found in edible bird's nest substance [134]. It is generally stated that sialic acid is not found in insects; conclusive evidence has now been presented for its presence in Drosophila melanogaster through all stages of development [ 1401.…”