A new alkaloid (C₁₉H₂₁NO₃, mp 197-198°, [α]ᴰᵀ -254°) was isolated from Argemone munita Dur. & Hilg. subsp. rotundata (Rydb.) G. B. Ownb. and was shown to be 2,9-dimethoxy-3-hydroxypavinane (I) by total synthesis. The synthesis was accomplished by formation of the Reissert compound from 7-methoxyisoquinoline and 3-methoxy-4-benzyloxybenzyl chloride, conversion to the benzylisoquinoline, N-methylation, reduction to the 1,2-dihydroisoquinoline, and cyclization to I with HCOOH and H₃PO₄. If the latter three steps were carried out on 1-(4-methoxybenzyl)-6,7-dimethoxyisoquinoline, the final product under the HCOOH and H₃PO₄ conditions was not a pavinane alkaloid, but instead the rearranged product 3-(4-methoxybenzyl)-6,7-dimethoxy-1,2,3,4-tetrahydro-N-methylisoquinoline. 9-(6-Deoxy-α-L-mannofuranosyl)adenine (3) has been prepared by several synthetic procedures and completely structure proofed. It was concluded that the substance previously reported to be 3 really could not have been, based upon the differences in physical properties and the present structure proof. The most successful synthesis required conversion of 6-deoxy-1,5-di-O-benzoyl-2,3-O-isopropylidene-L-mannofuranose into 6-deoxy-1,2,3,5-tetra-O-benzoyl-L-mannofuranose in two steps, conversion of this into the glycosyl chloride with ethereal hydrogen chloride, and condensation of the latter with 6-benzamidochloromercuripurine in hot xylene. Removal of the blocking groups with sodium methoxide and purification via a picrate gave an 18% yield of 3. Other coupling procedures, such as the titanium tetrachloride method, gave rather complex, colored mixtures, which required extensive column chromatography to purify 3, and consequently lower yields. Attempts to prepare 3 following acetolysis of 6-deoxy-1,5-di-O-acetyl-2,3-O-isopropylidene-L-mannofuranose (4) resulted in the isolation of 9-(6-deoxy-β-L-glucofuranosyl)adenine (5) and 9-(6-deoxy-p-L-mannopyranosyl)adenine (6) in addition to 3. Considerable yields of 5 occurred even under acetolysis reaction conditions that are reportedly not supposed to cause epimerization at C-2. Acetolysis of 4 in 1:1 acetic acid-acetic anhydride with 3% sulfuric acid, followed by nucleoside formation by the titanium tetrachloride procedure, afforded 5, 3, and 6 in a ratio of 1.5:2.2:1.0 and acetolysis of 4 in 3:7 acetic acid-acetic anhydride with 5% sulfuric acid changed this ratio to 0.1:1.5:1.0.