Two new types of oxindole alkaloids, salacin (1) and 3-oxo-7-hydroxy-3,7-secorhynchophylline (2), were isolated from the stem bark and hooks of the Thai medicinal plant Uncaria salaccensis along with three known oxindole alkaloids (rhynchophylline, isorhynchophylline, and corynoxine). The methanol extract was purified using DIAION HP-20 column chromatography without acid-base pretreatment, followed by silica gel columns (open, flash, HPLC). The structures of the new alkaloids were elucidated by UV, MS, ¹H-NMR, and NOE spectroscopy. The relative stereochemistry of salacin (1) was confirmed by NOE experiments and comparison with a synthetic stereoisomer. Laboratory synthesis of (±)-salacin (5) was achieved via Grignard reaction, benzylation, condensation with oxytryptamine, formylation, deprotection, and Swern oxidation; the synthetic product (except optical properties) was identical to natural salacin. 3-Oxo-7-hydroxy-3,7-secorhynchophylline (2) was synthesized from rhynchophylline or isorhynchophylline through MCPBA oxidation, modified Polonovski reaction, elimination, and CuCl₂-catalyzed oxidation. Complete spectroscopic (500 MHz ¹H-NMR, CD) identity between synthetic and natural 2 confirmed its stereochemistry and absolute configuration.