what is the structure of bamboo kun?
It is not implausible that bamboo should have antibacterial properties, after all plants generate lots of protective chemicals. However, the use of this particular word (kun or kunh) by a number of commercial textile websites seems like a promotional gimmick without a strong scientific basis.

Claims of an intrinsic antimicrobial property of processed bamboo fibers are likely exaggerated, as the excerpt below (1) suggests:


  3.3. Antibacterial Properties
  
  The antibacterial properties of the control sample (OB) and the
  composites (ZB, GB, ZGB) were qualitatively investigated by the
  bacteriostatic circle method against one Gram-negative (E. coli) and
  one Gram-positive (B. subtilis), and the results were shown in Figure
  6. Figure 6A displayed the antibacterial activities of bamboo samples against E. coli. It can be observed that OB had little antibacterial
  activity without an inhibition zone.


This is not to say that bamboo lacks antimicrobial properties. Plants employ a myriad of chemical substances as sources of physical and chemical protection. Extracts of bamboo (2) apparently contain bactericidal compounds, although the concentration in processed fibers appears insufficient to grant these significant antibacterial properties.

It's also worth adding that the above refer to specific species of bamboo and there may be significant variety in antibacterial properties across species. 

In conclusion it is difficult if not impossible to answer the OPs question as it is unclear what "kun" or "kunh" refers to, it may just be a catchphrase to describe unknown substances granting antibacterial properties to raw bamboo.

References


Junyi Zhang, Bo Zhang, Xiufang Chen, Bingbing Mi, Penglian Wei, Benhua Fei, and Xindong Mu. Antimicrobial Bamboo Materials Functionalized with ZnO and Graphene Oxide Nanocomposites. Materials (Basel). 2017 Mar; 10(3): 239.
doi: 10.3390/ma10030239
The origin of the antibacterial property of bamboo. T. Afrin , T. Tsuzuki , R.K. Kanwar &amp; X. Wang.  The Journal of The Textile Institute. 2012; 103(8): 844-8491. doi: 10.1080/00405000.2011.614742