Ring-Modified Analogues and Molecular Dynamics Studies To Probe the Requirements for Fungicidal Activities of Malayamycin A and Its N-Nucleoside Variants

1,3-Bifunctional Nucleophilic Allylation Reagents: Preparative Methods and Synthetic Applications

1,3-Bifunctional nucleophilic allylation reagents play an important role in organic synthesis. In this short review, we summarize the methods for the preparation of 1,3-bifunctional reagents and their reactions with various electrophiles. Synthetic applications of these reagents in the context of complex molecule synthesis are also discussed.

1 Introduction

2 Reagent Synthesis

2.1 Symmetrical Reagents

2.2 Unsymmetrical Reagents

2.2.1 Bis-silane and Silyl-stannane Reagents

2.2.2 Bis-boron and Silyl-boron Reagents

3 Synthetic Applications

3.1 Allylation of Aldehydes

3.2 Allylation of Ketones

3.3 Allylation of Imines

3.4 Allylation of Other Electrophiles with 1,3-Bifunctional Allylation Reagents

4 Summary

Synthesis of a pseudodisaccharide α-C-glycosidically linked to an 8-alkylated guanine

The synthesis of stable guanofosfocin analogues has attracted considerable attention in the past 15 years. Several guanofosfocin analogues mimicking the three constitutional elements of mannose, ribose, and guanine were designed and synthesized. Interest in ether-linked pseudodisaccharides and 8-alkylated guanines is increasing, due to their potential applications in life science. In this article, a novel guanofosfocin analogue 6, an ether-linked pseudodisaccharide connected α-C-glycosidically to an 8-alkylated guanine, was synthesized in a 10-longest linear step sequence from known diol 13, resulting in an overall yield of 26%. The key steps involve the ring-opening of cyclic sulfate 8 by alkoxide generated from 7 and a reductive cyclization of 4-N-acyl-2,4-diamino-5-nitrosopyrimidine 19 to form compound 6.

1,2;5,6-Di-O-isopropyl-idene-3-C-nitro-methyl-α-d-allofuran-ose

The mol­ecule of the title compound, C₁₃H₂₁NO₈, consists of two methyl­enedi­oxy rings and one tetra­hydro­furan ring. In the crystal, inter­molecular O—H⋯O hydrogen bonds link the mol­ecules into helical chains running along the 6₁ screw axis. Weak inter­molecular C—H⋯O hydrogen bonds help to stabilize the crystal packing. Voids of 245 ų per unit cell occur.

Synthesis of (-)-deoxoprosophylline, (+)-2-epi-deoxoprosopinine, and (2R,3R)- and (2R,3S)-3-hydroxypipecolic acids from D-glycals

New syntheses of (-)-deoxoprosophylline, (+)-2-epi-deoxoprosopinine, and (2R,3R)- and (2R,3S)-3-hydroxypipecolic acids are reported. Utilization of the chiral functionalities of Perlin aldehydes, derived from 3,4,6-tri-O-benzyl glycals, has been done along with chemoselective saturation of olefins and reductive aminations as key steps.

Trehalose biosynthesis is involved in sporulation of Stagonospora nodorum

Stagonospora nodorum is a necrotrophic fungal pathogen that is the causal agent of leaf and glume blotch on wheat. S. nodorum is a polycyclic pathogen, whereby rain-splashed pycnidiospores attach to and colonise wheat tissue and subsequently sporulate again within 2-3weeks. As several cycles of infection are needed for a damaging infection, asexual sporulation is a critical phase of its infection cycle. A non-targeted metabolomics screen for sporulation-associated metabolites identified that trehalose accumulated significantly in concert with asexual sporulation both in vitro and in planta. A reverse-genetics approach was used to investigate the role of trehalose in asexual sporulation. Trehalose biosynthesis was disrupted by deletion of the gene Tps1, encoding a trehalose 6-phosphate synthase, resulting in almost total loss of trehalose during in vitro growth and in planta. In addition, lesion development and pycnidia formation were also significantly reduced in tps1 mutants. Reintroduction of the Tps1 gene restored trehalose biosynthesis, pathogenicity and sporulation to wild-type levels. Microscopic examination of tps1 infected wheat leaves showed that pycnidial formation often halted at an early stage of development. Further examination of the tps1 phenotype revealed that tps1 pycnidiospores exhibited a reduced germination rate while under heat stress, and tps1 mutants had a reduced growth rate while under oxidative stress. This study confirms a link between trehalose biosynthesis and pathogen fitness in S.nodorum.

Malayamycin, a new streptomycete antifungal compound, specifically inhibits sporulation of Stagonospora nodorum (Berk) Castell and Germano, the cause of wheat glume blotch disease

BACKGROUND

Malayamycin is a novel perhydrofuropyran C-nucleoside isolated from Streptomyces malaysiensis that shows promising antifungal activity, fully controlling a range of diseases when applied to plants at 100 microg mL(-1). The goal of this study was to determine the mode of action.

RESULTS

Malayamycin exhibited in vitro antifungal activity against Stagonospora nodorum (Berk) Castell & Germano, the cause of stagonospora nodorum blotch of wheat. Growth in liquid minimum medium was merely delayed at 50 microg mL(-1), but sporulation was suppressed by more than 50% by 10 microg mL(-1) of malayamycin. When applied to wheat seedlings 36 h prior to infection, 10 microg mL(-1) of malayamycin reduced lesion size and significantly reduced pycnidiation to only 5% of the non-treated level. A transcription factor gene, Mrg1 (malayamycin response gene) whose expression was upregulated by application of malayamycin, was identified. Both Mrg1 knockout and overexpression strains were created. These strains were fully pathogenic, suggesting that the expression of Mrg1 did not affect pathogenicity. Interestingly, a strain that expressed Mrg1 50 times more than wild type showed a significant reduction in sporulation. However, all the tested knockout and overexpression strains retained sensitivity to malayamycin.

CONCLUSIONS

Malayamycin is a new type of antifungal compound that acts primarily by inhibiting sporulation. Although Mrg1 may be involved in the sporulation process, it is not the major contributor for sporulation inhibition caused by malayamycin treatment.