How to convert Excel comments to ChemDraw .cdx?
Because you find these entries in a Excel workbook, it is likely that this spreadsheet was created with Chemdraw's add-in for Excel (company's demo) to embed chemical formulae:

(source).
to provide a bridge between the two worlds to display chemical libraries (promotional example, or manual chapter 13).  To use it, you need both access to Excel as well as ChemDraw.
The (part of the) string shown by you does not look like the typical content of the binary .cdx, nor the human readable .cdxml file which would be understood by openbabel, a program written in the intent to interconvert structure files used in chemistry (it may read .cdx; but read and write .cdxml) on a one-by-one basis (e.g., in a GUI), or programmatically (e.g., C, Python).
Maybe you may identify the author of the spreadsheet.  Or find support by the software's authors (for some years now by PerkinElmer) / add-in maintainers (e.g., on GitHub).  It is not obvious their format were readable by similar products (e.g., ChemAxon's JChem).