Complex sentence: Szent-Györgyi had isolated the chemical hexuronic acid from animal adrenal glands at the Mayo clinic, and suspected it to be the anti-scorbutic factor, but could not prove it without a biological assay.
Split into simpler sentences: Szent-Györgyi had isolated the chemical hexuronic acid from animal adrenal glands at the Mayo clinic. He suspected it to be the anti-scorbutic factor but could not prove it without a biological assay.