Benzyloxy Substituent Research Articles

Nucleophilic additions to N‐glycosylnitrones part IV Asymmetric synthesis of N‐hydroxy‐α‐aminophosphonic and α‐aminophosphonic acids

AbstractThe addition of phosphite anions and of tris(trimethylsilyl) phosphite (P(OSiMe3)3) to N‐glycosyl‐C‐arylnitrones was examined. While these nitrones proved inert towards the phosphite anions, they reacted with P(OSiMe3)3 under catalysis by Lewis acids. Thus, P(OSiMe3)3 reacted with the crystalline (Z)‐N‐glycosylnitrones 2 and 8 to give the optically active N‐hydroxy‐α‐aminophosphonic acids 4 and 10, respectively, and hence the α‐aminophosphonic acids 5 and 11 in yields up to 92% and with an enantiomeric excess (e.e.) up to 97% (Scheme 1). The absolute configuration of the phosphonates depend upon the nature and – in one case – upon the quantity of the catalyst (Figure). Upon catalysis by HCIO4 or Zn(OTF)2, p(OSiMe3)3 added to 2 to give, in both cases, the (+)‐(R)‐phenylphosphaglycine 5 (optical purity 79–84 and 90–93%, resp.). The optical purity (o.p.) was hardly influenced by the amount of these catalysts (0.02‐;1 equiv.). However, catalysis by ZnCl2 gave, with trace quantities of the catalyst, (–)‐(S)‐5 (o.p. 79%), while an equimolar amount of ZnCl2 yielded (+)‐(R)‐5 (o.p. 82%). The HClO4‐catalyzed addition of P(OSiMe3)3 to the nitrone 14 (Scheme 2) led to (+)‐(R)‐N‐hydroxyphosphavaline 15 (78%) and hence to (–)‐(R)‐phosphavaline 16 (71% from 14 e.e. 95%). Under conditions leading from the nitrones 2, 8, 14, and 20 (Schemes 1 and 2) predominantly to (R)‐α‐aminophosphonic acids, the addition of P(OSiMe3)3 to nitrone 18, possessing a benzyloxy substituent as an additional potential ligand for the catalyst, gave (S)‐phosphaserine 19. The addition of P(OSiMe3)3 to the nitrone 20, catalyzed by Zn(OTf)2, led to (+)‐(R)‐N‐hydroxyphosphamehionine 21 (71%, e.e. 77%) and hence to (–)‐(R)‐phosphamethionine 22 (77% from 20, e.e. 79%). Catalysis by trace quantities of ZnCl2 gave (+)‐(S)‐22 (85%, e.e. 61%). The enantiomerically pure aminophosphonic acids 5, 11, and 16 were obtained by recrystalliztion. The e.e. of the N‐hydroxyaminosphosphonic acids 10, 15, and 21 and the aminophosphonic acids 5, 11, 16, and 22 were determined by the HPLC analysis of the dimethyl N‐naphthoyl‐α‐aminophosphonats 7, 13, 17, and 23, on a chiral stationary phase.

Quantitative structure-activity studies of benzoylphenylurea larvicides: II. Effect of benzyloxy substituents at aniline moiety against Chilo suppressalis Walker

The larvicidal activity of a series of N-2,6-difluorobenzoyl- N′-[4-(substituted benzyloxy)-phenyl]-ureas against nondiapause larvae of the rice stem borer, Chilo suppressalis Walker, was measured by a topical application method under conditions in which oxidative metabolism was inhibited by piperonyl butoxide. The effects of the substituted-benzyloxy moiety on variations in the activity were analyzed quantitatively using physicochemical substituent parameters and regression analysis. Results were compared with those found previously for N-2,6-difluorobenzoyl- N′-(4-substituted phenyl)-ureas, indicating that the electron-withdrawing property of the anilide substituents participates in determining the activity through the inductive effect. The hydrophobicity of the total anilide substituents favors activity, whereas the steric dimension in terms of the width lowers it. Although inhibition of new cuticle formation on cultured integument of diapausing larva could not be determined accurately for most of the compounds because of their limited solubility in the assay medium, inhibitory activity seemed related to larvicidal activity, as was the case for previously investigated simpler congeners.

Proton spin-lattice relaxation-rates and nuclear Overhauser enhancement, in relation to the stereochemistry of β- d-mannopyranose 1,2-orthoacetates

Data are reported on spin-lattice relaxation-rates and nuclear Overhauser enhancement of protons of exo and endo diastereoisomers of 1,2- O-(1-methoxyethylidene) and 1,2- O-(1-benzyloxyethylidene) derivatives of 3,4,6-tri- O-acetyl-β- d-mannopyranose, and of some specifically deuterated analogs of these derivatives. The results verified assignments of the orientation at the quaternary carbon atom of the acetal ring, and yielded information about the orientations favored by the exocyclic C-methyl and benzyloxy substituents.