Cuautepestalorin (4), a 7,8-dihydrochromene-oxoisochromane adduct bearing a spiro-polycyclic (6/6/6/6/6/6) ring system, along with its putative biosynthetic precursors, cytosporin M (1), cytosporin N (2), and oxopestalochromane (3), were isolated from the bioactive extract of Pestalotiopsis sp. using a combination of molecular networking and dereplication techniques. Their structures were elucidated using a set of spectroscopic, spectrometric, chiroptical (experimental and theoretical), and X-ray crystallography data. Compounds 3 and 4 exhibited modest potency when evaluated in vitro as α-glucosidase inhibitors.