The Journal of Antibiotics (2016) 69, 337–339 & 2016 Japan Antibiotics Research Association All rights reserved 0021-8820/16 www.nature.com/ja NOTE The enantioselective synthesis and biological evaluation of chimeric promysalin analogs facilitated by diverted total synthesis Kyle W Knouse and William M Wuest The Journal of Antibiotics (2016) 69, 337–339; doi:10.1038/ja.2016.4; published online 10 February 2016 The biosynthesis and subsequent modification of fatty acids plays a and pharmacological properties of migrastatin9 and epothilone,10 major role in the primary and secondary metabolism of both leading to viable drug candidates. In a similar fashion, the Reddy terrestrial and marine organisms. One such metabolite, myristic group applied DTS toward the synthesis of hybrid hermitamides, acid (1) is the biosynthetic precursor of a number of secondary derived from the coupling of lyngbic acid, a marine metabolite, with metabolites, four of which are depicted in Figure 1 (2–5). These amines from the terrestrial amides of the Piperaceae family resulting in molecules have each been shown to possess a broad range of compounds with in vitro cytotoxicity against human cancer cell lines.11 antibacteral and antivirulence activity ranging from the inhibition of Taking inspiration from these examples, we sought to utilize DTS biofouling and biofilm formation to the disruption of quorum-sensing through the coupling of a readily available precursor from our networks (vide). Our laboratory has recently completed the first total promysalin synthesis, ( − )-6S, with the structurally similar alcohol synthesis of promysalin ((− )-2), which confirmed both its absolute variants of lyngbic acid and the hermitamides. Herein, we report the stereochemistry and potent species-specific antibacterial activity (sub- biological evaluation and an enantioselective synthesis of both micromolar activity against P. aeruginosa).1,2 In 1978 Moore et al.3 enantiomers of lyngbic acid and hermatidamides A and B, and a identified lyngbic acid, (( − )-3) as a major component of the lipid focused library of chimeric promysalin derivatives. extracts from the marine cyanobacteria Lyngbya majuscula. Gerwick The synthesis of lyngbic acid began with the asymmetric allylation later studied the biological properties of this secondary metabolite and of octanal with allyltributylstannane mediated by a titanium-BINOL reported that ( − )-3 displays antimicrobial activity toward Gram- complex to afford either stereoisomer of allylic alcohol 7 (Scheme 1).12 positive bacteria (Staphylococcus aureus and Bacillus subtilis); however, Methylation of 7 followed by homologation via cross metathesis with Gram-negative strains were not evaluated.4 Additionally, ( − )-3 was 4-pentenoic acid affords both enantiomers of lyngbic acid (3)inan shown to interfere with the CqsS-mediated signaling pathway that is overall yield of 32%. The total syntheses of hermitamide A and B responsible for quorum sensing in Vibrio harveyi5 and inhibit the was accomplished by HATU-mediated coupling of 3 and phenylethy- growth of marine fungi Fusarium sp., Lindra thalassiae and Dendry- lamine to afford 4 or tryptamine to provide 5 in a longest linear phiella salina.6 In 2000, Gerwick et al.7 reported the isolation of two sequence of four steps. aromatic amide derivatives of lyngbic acid, hermitamides A (( − )-4) We next focused our attention toward the DTS of chimeric and B (( − )-5). These compounds were shown to be inhibitors of the molecules which required intermediate ( − )-6S, which was prepared human voltage-gated sodium channel,8 cytotoxic to neuro-2a neuro- as previously reported,4 and seco-acid 8 (available via cross blastoma cells and active in a brine shrimp toxicity assay.7 As with metathesis). Compound 8 was either treated with (2-(trimethylsilyl) lyngbic acid, these compounds were not evaluated against Gram- ethoxy)methyl chloride to afford the protected ester or HATU and the negative pathogens. Motivated by our earlier work on promysalin and respective amine to furnish the corresponding amides (10)and(11). the dire need for the discovery of novel therapeutics to combat The alcohols were then coupled to ( − )-6S using Shiina conditions13 Pseudomonas infections, we sought to investigate the potential of these and globally deprotected to provide the three sets of chimeric molecules as species-specific antibacterial agents. molecules: promysalin–lyngbic acid (12), promysalin–hermitamide A Similar to diversity-oriented synthesis, diverted total synthesis (13) and promysalin–hermitamide B (14) in a longest linear sequence (DTS) is a method by which one can leverage achievements in total of five steps. synthesis to access structural space, which is not possible through The antibacterial activity of the six classes of molecules (3–5, 12–14) biosynthetic means. Pioneering work by the Danishefsky group against a panel of four Gram-negative bacteria (two strains of demonstrated that DTS could be used to improve both the efficacy P. aeruginosa (PAO1, PA14), P. fluorescens,andP. putida)at Department of Chemistry, Temple University, Philadelphia, PA, USA Dedicated to Professor Amos B Smith, III, in recognition of his outstanding contributions to the fields of natural products and total synthesis. Correspondence: Professor WM Wuest, Department of Chemistry, Temple University, 1901 N. 13th Street, Philadelphia, PA 19122, USA. E-mail: [email protected] Received 10 December 2015; revised 12 January 2016; accepted 14 January 2016; published online 10 February 2016 Enantioselective synthesis and evaluation of chimeric promysalin analogs KW Knouse and WM Wuest 338 concentrations ranging from 455 nM–900 μM was next investigated (see O N Supplementary Table S1). To our surprise, only one analog ((+)-12R, HO C7H15 S) displayed antibacterial activity against all strains tested with an IC 1 OH O 50 Myristic Acid ( ) O O OH of 455 μM, ~1000-fold less active than ( − )-2. As one might expect, H2N 12R,S C6H13 the absolute stereochemistry of (+)- is identical to that of 2 O Promysalin ((-)- ) promysalin, reconfirming the role of those stereocenters in antibacter- O OMe ial activity. Curiously, during the course of our assays (at 48 h) we noticed a pronounced, non-lethal species-specific R C7H15 OH phenotype against PA14 (the strain that is most sensitive to the Lyngbic Acid ((-)-3): R = OH 6S Ph (-)- N activity of promysalin) when dosed with compounds ( − )-13R,S and Hermitamide A ((-)-4): R = N H NH O − 14S,S O ( )- (Supplementary Figure S1). This may hint at a disparate Hermitamide B ((-)-5): R = N H mechanism of action unrelated to antibacterial activity and is currently OSEM being investigated in our laboratory. In summary, we have reported a concise, enantioselective total Diverted Total Will chimera molecules retain Synthesis synthesis of the marine secondary metabolites lyngbic acid, antimicrobial activity? hermitamide A and hermitamide B. Furthermore, we utilized DTS to construct a focused library of six chimeric promysalin analogs Figure 1 Natural products derived from myristic acid and proposed diverted to further evaluate the structure–activity relationship of this total synthesis of chimera analogs. species-specific natural product. Our biological assays show, for the Ph O OMe HATU, DIEA, O OMe Amine N C7H15 HN C7H15 H Ph NH2 NH Hermitamide A NH2 HN Hermitamide B (-)- 4S: 84% (-)-5 S: 42% (+)-4R: 86% (+)-5 R: 64% 1) NaH, MeI O OMe OH 2) 4-Pentenoic Acid, Grubbs II HO C7H15 C7H15 (-)-7 S Lyngbic Acid (+)-7 R (-)-3S: 45% over 2 steps (+)-3 R: 38% over 2 steps 4-Pentenoic Acid, Hoveyda-Grubbs II 1) SEMCl, Et3N N O OH 2) (-)-6 S, MNBA, N TBAF, DMPU DMAP, Et3N HO O HO C7H15 SEMO O O O O (+)-8S: 72% O O O (-)-8 R: 67% HO C H C H 7 15 SEMO 7 15 Promysalin-Lyngbic Acid (-)-9S,S: 55% over 2 steps (-)-12S,S: 74% (+)-9R,S: 21% over 2 steps (+)-12 R,S: 89% N HATU, DIEA, 1) (-)-6 S, MNBA, O OH HO O Ph DMAP, Et N Ph NH 3 O O O 2 2) TBAF, DMPU HN C7H15 Ph (+)-10S: 84% N C7H15 H HATU, DIEA, (-)-10 : 86% R Promysalin-Hermitamide A NH NH 2 (-)-13S,S: 60% over 2 steps (-)-13 R,S: 49% over 2 steps O OH 1) (-)-6 S, MNBA, N DMAP, Et N HN HN C7H15 3 2) TBAF, DMPU HO O O (+)-11 S: 42% O O (-)-11 R: 64% N C7H15 H N H Promysalin-Hermitamide B (-)-14 S,S: 32% over 2 steps (+)-14 R,S: 28% over 2 steps Scheme 1 Synthesis of lyngbic acid (3), hermitamides A (4)andB(5) and chimeric compounds. For clarity only one stereoisomer is depicted and represented by the top compound name. The Journal of Antibiotics Enantioselective synthesis and evaluation of chimeric promysalin analogs KW Knouse and WM Wuest 339 first time, that lyngbic acid and the hermitamides do not possess any 3 Cardellina, J. J., Dalietos, D., Marner, F., Mynderse, J. S. & Moore, R. E. ( − )-Trans-7 significant antibacterial activity against a panel of Gram-negative (S)-methoxytetradec-4-enoic acid and related amides from the marine cyanophyte Lyngbya majuscula. Phytochemistry 17, 2091–2095 (1978). bacteria. Finally, we have demonstrated that subtle structural changes 4 Gerwick, W. H., Reyes, S. & Alvarado, B. Two malyngamides from the Caribbean to the promysalin side chain significantly reduce the biological activity cyanobacterium Lyngbya majuscula. Phytochemistry 26, 1701–1704 (1987). 5 Meyer, J. L., Gunasekera, S. P., Scott, R. M., Paul, V. J. & Teplitski, M. Microbiome of the natural product. shifts and the inhibition of quorum sensing by black band disease cyanobacteria. ISME J 10,1204–1216 (2016). 6 Soares, A. R., Engene, N., Gunasekera, S. P., Sneed, J. N. & Paul, V. J. Carriebowlinol, CONFLICT OF INTEREST an antimicrobial tetrahydroquinolinol from assemblage of marina cyanobacteria contain- – The authors declare no conflict of interest. ing a novel taxon. J. Nat. Prod. 78,534 538 (2015). 7 Tan, L. K., Okino, T. & Gerwick, W. H. Hermitamides A and B, Toxic Malyngamide-Type Natural products from the marine cyanobacterium Lyngbya majuscula.