U.S. Department of Health and Human Services

Carbohydrates Section

Paul Kovac, Ph.D., Dr. h.c., Chief

Section Staff

Photo of Peng Xu

Peng Xu, Research Fellow since 2010

Ph.D., Peking Union Medical College, Beijing, China, 2010
Thesis: Synthesis and structure-activity relationship study of macrolide derivatives with novel saccharide substituents
Advisor: Ping-Sheng Lei, Ph.D.

B.Sc., West China University of Medical Sciences, Sichuan, China, 2002

Current Project: Conjugation of amine-containing substances by squaric acid chemistry, and identification of variables that affect the conjugation efficiency. Use of the optimized protocol to make glycoconjugate vaccines for infectious diseases from bacterial antigens.


  • Peng Xu, Michael N. Trinh, Pavol Kovac. Conjugation of carbohydrates to proteins using di(triethylene glycol monomethyl ether) squaric acid ester revisited. Carbohydr. Res., 2018, 456, 24-29.
  • Peng Xu, Meagan Kelly, Willie F. Vann, Firdausi Qadri, Edward T. Ryan, Pavol Kovac. Conjugate vaccines from bacterial antigens by squaric acid chemistry: a closer look. ChemBioChem, 2017, 18(8), 799-815.
  • Divya Kushwaha, Peng Xu, Pavol Kovac. Carbohydrates as potentially versatile core subcarriers for multivalent immunogens. RSC Advances, 2017, 7(13), 7591-7603.
  • Pavol Kovac, Peng Xu. Controlled and highly efficient preparation of carbohydrate-based vaccines: squaric acid chemistry is the way to go. Royal Society of Chemistry Specialist Periodical Report, Carbohydrate Chemistry, 2017vol.42, 83-115.
  • Wilfredo R. Matias, Brie Falkard, Richelle C. Charles, Leslie M. Mayo-Smith, Jessica E. Teng, Peng Xu, Pavol Kovac, Edward T. Ryan, Firdausi Qadri, Molly F. Franke, Louise C. Ivers, Jason B. Harris. Antibody secreting cell responses following vaccination with bivalent oral cholera vaccine among Haitian adults. PLoS Negl. Trop. Dis, 2016, June 16.
  • Peng Xu, Edwin D. Stevens, Alfred D. French, Pavol Kovac. Synthesis and molecular structure of the 5-methoxycarbonylpentyl α-glycoside of the upstream, terminal moiety of the O-specific polysaccharide of Vibrio cholerae O1, serotype Inaba. Molecules, 2015, 20, 2892-2902.
  • Louise C. Ivers, Richelle C. Charles, Isabelle J. Hilaire, Leslie M. Mayo-Smith, Jessica E. Teng, J Gregory Jerome, Jenna Rychert, Regina C. LaRocque, Peng Xu, Pavol Kovac, Edward T. Ryan, Firdausi Qadri, Charles P. Almazor, Molly F. Franke, Jason B. Harris. Immunogenicity of the bivalent oral cholera vaccine Shanchol in Haitian adults with HIV infection. J. Infect. Dis., 2015, first published online Feb.26th, 2015.
  • Peng Xu, Sayantan Bhaduri, Pavol Kovac. Isopropyl 2,3,4,6-tetra-O-benzoyl-1-thio-β-D-galactopyranoside, a convenient galactosyl donor, in Carbohydrate chemistry: Proven synthetic methods, Ed. Rene Roy, Sebastien Vidal, Vol. 3. Chapter 29, 227-234, 2015.
  • Peng Xu, Zbigniew Dauter, Pavol Kovac. Synthesis, characterization, and crystal structure of sodium (methyl α-D-mannopyranosid)uronate monohydrate. Synthesis, 2014, 46, 1073-1078.
  • Mohammad Murshid Alam, Megan Kelly Bufano, Peng Xu (co-first authors), Anuj Kalsy, Y. Yu, Y. Wu Freeman, Tania Sultana, Rasheduzzaman Rashu, Ishaan Desai, Grace Eckhoff, Daniel T. Leung, Richelle C. Charles, Regina C. LaRocque, Jason B. Harris, John D. Clements, Stephen B. Calderwood, Firdausi Qadri, W. F. Vann, Pavol Kovac, Edward T. Ryan. Evaluation in mice of a conjugate vaccine for cholera made from Vibrio cholerae O1 (Ogawa) O-specific polysaccharide. PLoS Negl. Trop. Dis, 2014, 8(2), 1-8.
  • Peng Xu, Riccardo Castelli, Pavol Kováč. Synthesis and characterization of tetra-O-propargyl Pentaerythritol. Carbohydrate chemistry: Proven synthetic methods, Vol. 2, 213-216, 2014.
  • Farid Jahouh, Peng Xu, Willie F. Vann, Pavol Kovac, Joseph H. Banoub. Mapping the glycation sites in the neoglycoconjugate from hexasaccharide antigen of Vibrio cholerae, serotype Ogawa and the recombinant tetanus toxin C-fragment carrier. J. Mass. Spectrom., 2013, 48(10), 1083-1090.
  • Daniel T. Leung, Taher Uddin, Peng Xu (co-first authors), Amena Aktar, Russell A. Johnson, Mohammad Arif Rahman, Mohammad Murshid Alam, Meagan Kelly Bufano, Grace Eckhoff, Ying Wu-Freeman, Yanan Yu, Tania Sultana, Farhana Khanam, Amit Saha, Fahima Chowdhury, Ashraf I. Khan, Richelle C. Charles, Regina C. LaRocque, Jason B. Harris, Stephen B. Calderwood, Pavol Kovac, Firdausi Qadri, Edward T. Ryan. Immune responses to the O-specific polysaccharide antigen in children who received a killed oral cholera vaccine compared to responses following natural cholera infection in Bangladesh. Clin. Vaccine Immunol., 2013, 20 (6), 780-788
  • Peng Xu, Pavol Kováč. Observations on the preparation of β-lactose octaacetate. Journal of Carbohydrate Chemistry, 2012, 31, 711-720.
  • Edward T. Ryan, Pavol Kováč, Firdausi Qadri, Peng Xu, Stephen B. Calderwood, Willie F. Vann, Dwight C. Peterson. Conjugating amines. 2012, WO2013009826.
  • Xiaozhuo Chen, Peng Xu, Yanpeng Xu, Lu Liu, Yi Liu, Di Zhu and Pingsheng Lei. Synthesis and antibacterial activity of novel modified 5-O-desosamine ketolides. Bioorg. Med. Chem. Lett. 2012, (22), 7402-7405
  • Russell Johnson, Taher Uddin, Amena Aktar, Md. Mohasin, Mohammad Murshid Alam, Fahima Chowdhury, Jason Harris, Regina LaRocque, Meagan Bufano, Yanan Yu, Ying Wu, Daniel Leung, David Sarracino, Bryan Krastins, Richelle Charles, Peng Xu, Paul Kováč, Stephen Calderwood, Firdausi Qadri, and Edward Ryan. Comparison of immune responses to the O-specific polysaccharide and lipopolysaccharide of Vibrio cholera O1 in Bangladeshi adult patients with cholera. Clin. Vaccine Immunol., 2012, 19 (11), 1712-1721.
  • Xiaozhuo Chen, Peng Xu, Lu Liu and Pingsheng Lei. Synthesis and antibacterial activities of novel ketolides with 11,12-sulfur contained aryl alkyl side chains. Euro. J. Med. Chem. 2011, 46(1), 208-217
  • Peng Xu, Mohammad Murshid Alam, Anuj Kalsy, Richelle C. Charles, Stephen B. Calderwood, Firdausi Qadri, Edward T. Ryan and Pavol Kováč. Simple, direct conjugation of bacterial O-SP–core antigens to proteins: Development of cholera conjugate vaccines. Bioconjugate Chemistry, 2011, 20(10), 2179-2185
  • Peng Xu, Lu Liu, Wei He, Yun Li, Jian Liu and Ping-Sheng Lei. Synthesis and antibacterial activity of 11,12-carbamate-3-O-acyl erythromycin derivatives. J. Asian Nat. Prod. Res. 2009, 11(10), 880-897
  • Peng Xu, Lu Liu, Xiao-Zhuo Chen, Yun Li, Jian Liu, Zhi-Ping Jin, Guang-Qiang Wang and Ping-Sheng Lei. Synthesis of novel macrolide derivatives with imidazo[4,5-b]pyridinyl sulfur contained alkyl side chains and their antibacterial activity. Bioorg. Med. Chem. Lett. 2009, (19), 4079-4083
  • Peng Xu, Lu Liu, Zhi-Ping Jin, Guang-Qiang Wang, Jian Liu, Yun Li and Ping-Sheng Lei. Synthesis and antibacterial activity of 4”-O-heteroarylcarbamoyl derivatives of macrolide. Bioorg. Med. Chem. Lett. 2008, (18), 5507-5511
  • Lu Liu, Peng Xu, Liang Zhou and Ping-Sheng Lei. Synthisis of derivatives of imidazo[4,5-b]pyridine: Novel sulfur contained side chains for macrolide antibiotics. Chin. Chem. Lett. 2008, (19), 1-4
  • Peng Xu, Lu Liu, Zhi-Ping Jin and Ping-Sheng Lei. Synthesis and antibacterial activity of derivatives of 6-O-allylic acylides. Bioorg. Med. Chem. Lett. 2007, (17), 3330-3334
  • Peng Xu, Yao Yang, Yang Shi, Lu Liu and Ping-Sheng Lei. Synthesis of derivatives of (9S)-9-hydroxyl-12-methylene erythromycin A and their antibacterial activity in vitro. Acta Pharmaceutica Sinica, 2007, 42(5): 497-501
  • Shu-Jie Hou, Peng Xu, Liang Zhou, De-Quan Yu and Ping-Sheng Lei. Synthesis and antitumor activity of icogenin and its analogue. Bioorg. Med. Chem. Lett. 2006, (16), 2454-2458
  • Ping-Sheng Lei, Peng Xu and Lu Liu. Advance in synthesis of ketolides, a new class of erythromycin derivatives. Acta Academiae Medicinae Sinicae, 2004, 26(4), 467-473

Personal Interests: photography, reading, hiking

Photo of Helene Pfister

Helene Pfister, Visiting Fellow since 2017

Ph.D., Institut Pasteur, Paris Descartes University, 2014
Synthesis of oligosaccharides related to the O-specific polysaccharide of Shigella sonnei
Advisor: Laurence A. Mulard, Ph.D.

MSc in Drug Discovery, University of London, 2011; BSc in Chemistry, University of Paris-Sud, 2008

Current Project: Synthesis of conjugation-ready multivalent glycan antigens (clusters) that display oligosaccharides related to the O-specific polysaccharide of V. cholerae and conjugation to BSA by squaric acid chemistry. Comparison of antigenicity of these conjugates with those of standard star-shaped neoglycoconjugates will improve our understanding of the importance of multivalency for antigenicity and immunogenicity of vaccine candidates.


  • Herrendorff, R.; Hänggi, P.; Pfister, H.; Yang, F.; Demeestere, D.; Hunziker, F.; Frey, S.; Schaeren-Wiemers, N.; Steck, A. J.; Ernst, B., Selective in vivo removal of pathogenic anti-MAG autoantibodies, an antigen-specific treatment option for anti-MAG neuropathy. Proc. Natl. Acad. Sci. U.S.A. 2017114 (18), E3689-E3698.
  • Pfister, H. B.; Mulard, L. A., Synthesis of the Zwitterionic Repeating Unit of the O-Antigen from Shigella sonnei and Chain Elongation at Both Ends. Org. Lett. 201416 (18), 4892-4895.
  • Hancock, R.; Schaap, M.; Pfister, H.; Wells, G., Peptide inhibitors of the Keap1-Nrf2 protein-protein interaction with improved binding and cellular activity. Org. Biomol. Chem201311(21), 3553-3557.

Personal Interests: traveling, reading, watching movies

Photo of Mana Mohan Mukherjee

Mana Mohan Mukherjee, Visiting Fellow

Ph.D., Jadavpur University, Kolkata, India, 2017
Thesis: Synthetic Studies On Various Carbohydrate Systems
Advisor: Dr. Rina Ghosh, Professor

M.Sc. University of Kalyani, Kalyani, Nadia, India, 2011,
B.Sc. Krishnath College, Berhampore, India, 2009

Current Project: Synthesis of large framents the O-specific polysaccharides of Vibrio cholerae O:1 and their conjugation to suitable protein carriers by squaric acid chemistry. The conjugates will be used to determine the minimum structural requirements in the Vibrio cholerae O:1 antigen to form a potent vaccine for cholera.


  • Synthetic Routes toward Acidic Pentasaccharide Related to the O-Antigen of E. coli 120 Using One-Pot Sequential Glycosylation Reactions. Mukherjee, M. M.; Ghosh, R. J. Org. Chem.201781, 5711-5760.
  • Efficient One-Pot Per-O-Acetylation-Thioglycosidation of Native Sugars, 4,6-O-Arylidenation and One-Pot 4,6-O-Benzylidenation-Acetylation of S-/O- Glycosides Catalyzed by Mg(OTf)2. Mukherjee, M. M.; Basu, N.; Chaudhury, A.; Ghosh, R. RSC Adv., 20166, 109301-109314.
  • Iron (III) Chloride Modulated Selective 1,2-trans Glycosylation Based on Trichloroacetimidate Donors and its Application in Orthogonal Glycosylation. Mukherjee, M. M.; Basu, N.; Ghosh, R. RSC. Adv., 20166, 105589-105606.
  • Expeditious Synthesis of the Tetrasaccharide Cap Domain of the Leishmania donovani Lipophosphoglycan Using One-Pot Glycosylation Reactions. Mukherjee, M. M.; Basu, N.; Ghosh, R. RSC. Adv., 20166, 45112-45119.
  • Synthetic Routes Towards the Trisaccharide Related to the Lipopolysaccharide of Burkholderia sp. HKI-402 (B4). Basu, N.; Mukherje, M. M.; Ghosh, R. RSC. Adv., 20144, 54084-54090.
  • Synthesis of Tri- and Tetra-Mannosides Based on Sequential One-Pot Three Component Glycosylation Reactions. Basu, N.; Mukherjee, M. M.; Chaudhury, A.; Ghosh, R. J. Ind. Chem. Soc.201390, 1815-1820 (Invited Article).

Personal Interests: Travelling, Photography

View photos of previous associates.