Herein we report the diastereoselective synthesis of a 3-amino-1,2,4-oxadiazine (AOXD) scaffold. The presence of a NO bond in the ring prevents the planar geometry of the aromatic system and induces a strong decrease in the basicity of the guanidine moiety. While DIBAL-H appeared to be the most efficient reducing agent because it exhibited high diastereoselectivity, we observed various behaviors of the Mitsunobu reaction on the resulting β-aminoalcohol, leading to either inversion or retention of configuration depending on the steric hindrance in the vicinitude of the hydroxy group. The physicochemical properties (pKa, and log D) and hepatic stability of several AOXD derivatives were experimentally determined and found that the AOXD scaffold possesses promising properties for drug development. Moreover, we synthesized alchornedine, the only natural product with the AOXD scaffold. Based on a comparison of the analytical data, we found that the reported structure of alchornedine was incorrect and hypothesized a new one. were screened for the diastereoselective synthesis of chiral AOXDs and the relationship between chirality and NMR characteristics was highlighted. As a novel scaffold, the physicochemical properties of AOXD were also investigated. Finally, alchornedine was synthesized, and its spectra and analytical data were compared with those of the isolated compound previously reported. 14 RESULTS AND DISCUSSION As an initial experiment, achiral N-Boc-glycine was used as the starting material for exploring the synthesis of racemic AOXD (Scheme 1). N-Boc-glycine reacted with N, N'-carbonyl diimidazole (CDI) and N,O-dimethylhydroxylamine to form the corresponding Weinreb amide (2) in 99% yield. 18 The nucleophilic addition between 2 and 3,4-dichloro-phenyl magnesium bromide furnished ketone 3 in 86% yield, which was directly reduced by NaBH4, to yield alcohol 4 in 99% yield. As a key step in AOXD synthesis, the Mitsunobu reaction between alcohol 4 and N-hydroxyphthalimide (NHPI) was conducted to form the CON bond, affording the key intermediate, 5, in 94% yield. Then, phthaloyl and Boc protections were successively removed by hydrazine hydrate and HCl treatments, affording 6 and 7 in 94% and 96% yield, respectively. Finally, the cyclization reaction of 7 was carried out with BrCN, to afford racemic AOXD 8 and its 4-cyanated side product 9 in 81% and 17% yield, respectively (see SI section I). The presence of such a side product indicated that the nitrogen atom at position 4 (-HN-CH2-) in 8 is more nucleophilic toward BrCN than those at positions 3 and 2, respectively. X-ray crystallography confirmed the AOXD structure of 8 (Scheme 1), with a C=N double bond located between N 2 and C 3 , rather than C 3 and N 4 , likely because of the stabilization of p-π conjugation between the oxygen atom and the C=N double bond. Meanwhile, the bivalent character of the oxygen atom induced the expected non-planar geometry of AOXD, in which C 6 is located far out of the plane constituted by the N 2 =C 3-N 4 moiety. Moreover, the N...