Investigation of the alkaloidal constituents of Buxus microphylla Sieb. et Zucc. var. suffruticosa Makino forma major Makinol led to the isolation of a new alkaloid, C27H48N2, m.p. 200-202', [α]D +76° (c, 1.09 in CHCl3), which contains no oxygen function. Its structure (Ia) was assumed based on biogenetic considerations and NMR signals (including four quaternary methyl groups at δ 8.87, 8.98, 9.03, 9.10 τ, etc.). Methylation of this alkaloid afforded the N,N'-dimethyl derivative (Ib), C29H50N2, m.p. 206-207', [α]D +31° (c, 0.54 in CHCl3). This derivative was synthesized from cyclomicrophylline-A via catalytic hydrogenation to dihydro derivative (IIIa), tosylation to ditosylate (IIIb), reaction with sodium benzylmercaptide to bis-benzyl thioether (IIIc), and desulphurization with Raney nickel, confirming identity by m.p., mixed m.p., rotation, and IR/NMR spectra. Ruschig degradation led to amino ketone (IV), m.p. 194', [α]D +14° (c, 0.82 in CHCl3), with a dimethylamino group (confirmed by NMR and trifluoroacetic acid shift) and a 4,4'-dimethyl-5-keto system (via Cotton effect and absence of methyl ketone signal), supporting the methylamino group at the F position. This alkaloid corresponds to "Alkaloid-L" from Buxus sempervirens, with conclusions consistent with those of Arigoni et al.