L proline pro

To modulate Ser, proline (Pro), and glycine (Gly) availability in the culture medium, we used a custom‐made RPMI medium without Gln, Ser, Pro, or Gly (Cell Culture Technologies) supplemented with 10 mmol/L HEPES (Gibco), 2 mmol/L Gln (Sigma), 1 mmol/L sodium pyruvate, penicillin/streptomycin (Thermo Fisher Scientific), and 0.5% heat‐inactivated FBS (Eurobio). L‐serine (Ser), L‐proline (Pro), and Gly hydrochloride solutions (Sigma) were added as indicated. B16‐OVA cells were first expanded in complete medium containing Ser, Pro, and Gly at a saturating concentration (200 µM). The cells were then seeded (2 × 10³ cells at 200 µL/well) in a flat‐bottom 96‐well plate at the indicated concentrations of Ser, Pro, and Gly. Four days later, the number of live DAPI^–annexin V^– cells was assessed by flow cytometry using 123count eBeads (Thermo Fisher Scientific).

The cationic dioxa 1 and azaoxa 2 [6]helicenes were synthesised with BF₄⁻ as the counterion according to ref. 35 (link). Their enantiomers were isolated through chiral stationary phase HPLC resolution.^{36 (link)} The electron donors, d- and l-tryptophan (d-Trp, 99% Acros Organics, l-Trp, 99% Fluka), (+)- and (−)1,1′-bi-2-naphthol (+)-(−)-BINOL, (99%, Alfa Aesar), l-proline (Pro, 99%, Sigma-Aldrich) and as well as the solvents, water (deionised, Sigma-Aldrich), acetonitrile (ACN, for spectroscopy, Acros Organics), ethanol (EtOH, Acroseal, Acros Organics), dichloromethane (DCM, Rotidry Sept, Carl Roth), and tetrahydrofuran (THF, for spectroscopy, Sigma-Aldrich) were of the highest purity commercially available and were used as received. N,N-Dimethyl-1-phenylethylamine (DMPEA, Sigma-Aldrich) was distilled before use.