Endo-pH

Guide (The following is our recommended protocol. This protocol is for guidance only and should be modified according to your specific needs).

1. Stock Solution Preparation
1.1 Solvent: Alternatives include DMSO[1], ethanol[2], or CH₂Cl₂[3].
1.2 Concentration recommendation:
1.2.1 0.1 mM when using DMSO as solvent[1].
1.2.2 100 nM when using ethanol as solvent[2].
1.2.3 Ketene stock solution generated in situ from 1.0 equiv of precursor (e.g., precursor 1) when using CH₂Cl₂ as solvent[3].

2. Working Solution Preparation
2.1 Diluent: Alternatives include DMEM containing 10% w/v FBS[1], or CH₂Cl₂[3].
2.2 Working concentration:
2.2.1 0.1 mM when using DMEM containing 10% w/v FBS as diluent (no dilution step from DMSO stock)[1].
2.2.2 2.0 equiv of alkene (e.g., 3, 6, 8); 2.5 equiv of EtAlCl₂ (for in situ generated ketene with Et₃NHCl byproduct); 1.5 equiv of EtAlCl₂ (for isolated/purified ketene); 1.1 equiv of Et₃N when using CH₂Cl₂ as diluent[3].
2.3 Note: Adjust working solution concentration as needed; prepare fresh before use.

3. Staining Procedure
3.1 For adherent mammalian cells (U2OS, HeLa, A549 cell lines)[1]:
3.1.1 Incubation conditions: Incubate cells with 0.1 mM Endo-pH (BODIPY 6) working solution at 37°C for 60 minutes.
3.1.2 Washing steps: Wash cells with DMEM containing 10% w/v FBS.
3.2 For adherent plant cells (rice scutellar epithelium cells)[2]:
3.2.1 Incubation conditions: Add 100 nM sodium monensin to preincubation and incubation media; incubate at 30°C.
3.2.2 Washing steps: No washing steps specified.
3.3 For small-molecule ketene and alkene solutions[3]:
3.3.1 Incubation conditions:
3.3.1.1 Ketene generation: Incubate precursor (e.g., 1) with Et₃N in CH₂Cl₂ at 22 °C for 1 h.
3.3.1.2 Lewis acid promoted cycloaddition: Add EtAlCl₂ to the ketene-alkene mixture, incubate from -78 °C to 22 °C for 1.5 h (or at -78 °C for 2-3 h).
3.3.1.3 Thermal cycloaddition: Incubate ketene-alkene mixture in toluene at 120 °C for 24 h, or in CH₂Cl₂ at 22 °C for 12 h.
3.3.2 Washing steps: No washing steps specified.

4. Controls
4.1 Negative controls (samples without Sodium Monensin (HY-N0150) treatment)[2].
4.2 Control experiments to confirm inversion in selectivity is not due to solvent effect[3].

5. Detection & Analysis
5.1 Instrument type: Fluorescence microscope[1], electron microscope[2], NMR spectrometer[3].
5.2 Ex/Em wavelengths: Ex 688 nm; Em 786 nm[1].
5.3 Result analysis:
5.3.1 Fluorescence intensity increases significantly in acidic environments (pH ~5.0); fluorescence localizes to late endosomes (co-localizes with Rab7-RFP marker); produces far-red/near-infrared fluorescence[1].
5.3.2 Golgi cisternae in treated cells show swelling while maintaining mutual adherence; characteristic intercisternal material is visible between Golgi saccules; treated cells have larger central vacuoles compared to control cells; rough endoplasmic reticulum does not show swelling in treated cells[2].
5.3.3 Determine product yield via ¹H NMR with an internal standard; determine diastereomeric ratio via ¹H NMR analysis of the unpurified reaction mixture; Lewis acid promoted conditions favor exo-Ph adducts (e.g., 7a, 9a) while thermal conditions favor endo-Ph adducts (e.g., 7b, 9b); increased steric bulk of ketene alkyl substituent enhances diastereoselectivity in Lewis acid promoted reactions; ketene with non-rotatable aryl ring forms endo-Ar adduct with excellent diastereoselectivity under both thermal and Lewis acid promoted conditions[3].