Publications

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Book Chapter
Moore, BS, Floss HG.  1999.  Biosynthesis of Cyclic Fatty Acids Containing Cyclopropyl-, Cyclopentyl-, Cyclohexyl-, and Cycloheptyl-rings. Comprehensive Natural Products Chemistry. ( Editors-in-Chief:  Otto M, Sir Derek B, Koji NakanishiA2 - Editors-in-Chief:  Otto Meth-Cohn S, Koji N, Eds.).:61-82., Oxford: Pergamon   http://dx.doi.org/10.1016/B978-0-08-091283-7.00002-3   Abstract
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Moore, BS.  1998.  "Biosynthetic Studies on the Salinamides, Depsipeptides from a Marine Streptomyces". New Developments in Marine Biotechnology. ( Le Gal Y, Halvorson HO, Eds.).:xvi,343p.., New York: Plenum Press Abstract
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McKinnie, SMK, Miles ZD, Moore BS.  2018.  Characterization and biochemical assays of Streptomyces vanadium-dependent chloroperoxidases. Marine Enzymes and Specialized Metabolism, Pt A. 604( Moore BS, Ed.).:405-424., San Diego: Elsevier Academic Press Inc   10.1016/bs.mie.2018.02.016   Abstract

Vanadium-dependent haloperoxidases (VHPOs) are fascinating enzymes that facilitate electrophilic halogen incorporation into electron-rich substrates, simply requiring vanadate, a halide source, and cosubstrate hydrogen peroxide for activity. Initially characterized in fungi and red algae, VHPOs were long believed to have limited regio-, chemo-, and enantioselectivity in the production of halogenated metabolites. However, the recent discovery of homologues in the biosynthetic gene clusters of the stereo-selectively halogenated meroterpenoids from marine-derived Streptomyces bacteria has revised this paradigm. Their intriguing transformations have both enhanced and contributed to the fields of synthetic organic and natural product chemistry. We, herein, describe the expression, purification, and chemical assays of two characterized vanadium-dependent chloroperoxidase enzymes (NapH1 and Mcl24), and one homologue devoid of chlorination activity (NapH3), involved in the biosyntheses of halogenated meroterpenoid products.

Floss, HG, Cho H, Casati R, Reynolds KA, Kennedy E, Moore BS, Beale JM, Mocek UM, Poralla K.  1992.  Diversions of the Shikimate Pathway — The Biosynthesis of Cyclohexanecarboxylic Acid. Secondary-Metabolite Biosynthesis and Metabolism. 44( Petroski R, McCormick S, Eds.).:77-88.: Springer US   10.1007/978-1-4615-3012-1_6   Abstract

The shikimic acid pathway1 has evolved in plants and microorganisms to provide for the synthesis of the aromatic amino acids, phenylalanine, tyrosine and tryptophan, as well as a number of other essential aromatic compounds, e.g., jo-aminobenzoic acid, the precursor of folic acid, or]D-hydroxybenzoic acid, the precursor of ubiquinone. A vast number of secondary metabolites, e.g., alkaloids or phenylpropanoids, are derived from these aromatic end products of the pathway. In addition, nature has invented a variety of diversions along the pathway which lead to a range of additional natural products. While the majority of secondary metabolites are derived from late segments of the shikimate pathway, at or beyond the stage of the branch point intermediate, chorismate, a few diversions also occur in the prechorismate part of the pathway. One of these, the reduction of shikimic acid to cyclohexanecarboxylic acid, forms the topic of this chapter.

Udwary, DW, Kalaitzis JA, Moore BS.  2008.  Emerging marine biotechnologies – Cloning of marine biosynthetic gene clusters. Oceans and human health. ( Walsh PJ, Smith SL, Fleming LE, Solo-Gabriele HM, Gerwick WH, Eds.).:507-524., Amsterdam ; Boston: Elsevier Abstract
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Moore, BS.  2002.  The Interface of Natural Product Chemistry and Biology. Marine biotechnology in the twenty-first century : problems, promise, and products. ( on of Products. N(US), Ed.).:61-64., Washington, DC: National Academy Press Abstract
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Floss, HG, Kim CG, Moore BS.  1995.  New Variants of the Shikimate Pathway in the Biosynthesis of Antibiotics and Other Microbial Metabolites. Sekundärmetabolismus Bei Mikroorganismen: Beiträge Zur Forschung. ( Kuhn W, Fiedler HP, Demain AL, Eds.)., Tübingen, Germany: Attempto-Verlag Abstract
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Roberts, AA, Ryan KS, Moore BS, Gulder TAM.  2010.  Total (Bio)Synthesis: Strategies of Nature and of Chemists. Natural Products Via Enzymatic Reactions. 297( Piel J, Ed.).:149-203., Berlin: Springer-Verlag Berlin   10.1007/128_2010_79   Abstract

The biosynthetic pathways to a number of natural products have been reconstituted in vitro using purified enzymes. Many of these molecules have also been synthesized by organic chemists. Here we compare the strategies used by nature and by chemists to reveal the underlying logic and success of each total synthetic approach for some exemplary molecules with diverse biosynthetic origins.

Conference Proceedings
Doi-Katayama, Y, Tang L, Park C, Yu TW, Moore BS, Floss HG, Hutchinson CR.  1999.  Biosynthesis of the Ansamycin Antibiotic Rifamycin: Polyketide Synthase Processes Multiple Polyketide Chains Simultaneously. Symposium on the Chemistry of Natural Products. 41:637-642., Japan Abstract

The assembly of the polyketide backbone of rifamycin B on the type I rifamycin polyketide synthase(PKS), encoded by the rifA-rifE genes, is terminated by the product of the rifF gene, an amide synthase that releases the completed undecaketide as its macrocyclic lactam. Inactivation of rifF demonstrats that the PKS operates in a processive manner. Whereas the tetraketide carries an unmodified aromatic chromophore, the penta- through decaketide have undergone oxidative cyclization to the naphthoquinone, suggesting that this modification occurs during, not after, PKS assembly. The structure of one of the accumulated compounds together with 18O experiments suggests origin 8-OH groupe of 8-hydroxy-7,8-dihydronaphthoquinone. Inaction of the rifR gene that encodes a thioesterase II-like protein shows it is unlikely that the RifR thioesterase catalyzes their release to a major extent.

Journal Article
Moore, BS, Floss HG, Poralla K.  1995.  3 New Omega-Cycloheptyl Fatty-Acids from Alicyclobacillus-Cycloheptanicus and Their Biosynthetic Interrelationships. Journal of Natural Products-Lloydia. 58:590-593.   10.1021/np50118a019   AbstractWebsite

Three minor omega-cycloheptyl fatty acids from Alicyclobacillus cycloheptanicus have been identified as omega-cycloheptylnonanoate, -decanoate, and -alpha-hydroxytridecanoate. The biosynthetic interrelations of these cyclic fatty acids have been studied, C-13-Labeled omega-cycloheptylundecanoate and -alpha-hydroxyundecanoate were converted to omega-cycloheptyldecanoate, which is one carbon shorter in length. alpha-Hydroxylation of omega-cycloheptylundecanote was also observed, but not chain extension to omega-cycloheptyltridecanoate.

Moore, BS, Chen JL, Patterson GML, Moore RE, Brinen LS, Kato Y, Clardy J.  1990.  7.7 Paracyclophanes from Blue-Green-Algae. Journal of the American Chemical Society. 112:4061-4063.   10.1021/ja00166a066   AbstractWebsite
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Moore, BS, Eustaquio AS, McGlinchey RP.  2008.  Advances in and applications of proteasome inhibitors. Current Opinion in Chemical Biology. 12:434-440.   10.1016/j.cbpa.2008.06.033   AbstractWebsite

With the recent US Food and Drug Administration approval of bortezomib (Velcade(R)) for the treatment of relapsed multiple myeloma, the proteasome has emerged as a new therapeutic target with diverse pathology. Drug discovery programs in academia and the pharmaceutical industry have developed a range of low nanomolar synthetic and natural inhibitors of the 20S proteasome core particle that have entered human clinical trials as significant anti-cancer and anti-inflammatory leads. Moreover, proteasome inhibitors continue to serve as valuable research tools in cellular biology through the elucidation of important biological processes associated with the ubiquitin-proteasome pathway of protein degradation. This review will highlight recent advances in the development and application of proteasome inhibitors.

Niewerth, D, Jansen G, Riethoff LFV, van Meerloo J, Kale AJ, Moore BS, Assaraf YG, Anderl JL, Zweegman S, Kaspers GJL, Cloos J.  2014.  Antileukemic activity and mechanism of drug resistance to the marine Salinispora tropica proteasome inhibitor Salinosporamide A (Marizomib). Molecular Pharmacology. 86:12-19.   10.1124/mol.114.092114   AbstractWebsite

Salinosporamide A (NPI-0052, marizomib) is a naturally occurring proteasome inhibitor derived from the marine actinobacterium Salinispora tropica, and represents a promising clinical agent in the treatment of hematologic malignancies. Recently, these actinobacteria were shown to harbor self-resistance properties to salinosporamide A by expressing redundant catalytically active mutants of the 20S proteasome beta-subunit, reminiscent of PSMB5 mutations identified in cancer cells with acquired resistance to the founding proteasome inhibitor bortezomib (BTZ). Here, we assessed the growth inhibitory potential of salinosporamide A in human acute lymphocytic leukemia CCRF-CEM cells, and its 10-fold (CEM/BTZ7) and 123-fold (CEM/BTZ200) bortezomib-resistant sublines harboring PSMB5 mutations. Parental cells displayed sensitivity to salinosporamide A (IC50=5.1 nM), whereas their bortezomib-resistant sublines were 9-and 17-fold cross-resistant to salinosporamide A, respectively. Notably, combination experiments of salinosporamide A and bortezomib showed synergistic activity in CEM/BTZ200 cells. CEM cells gradually exposed to 20 nM salinosporamide A (CEM/S20) displayed stable 5-fold acquired resistance to salinosporamide A and were 3-fold cross-resistant to bortezomib. Consistent with the acquisition of a PSMB5 point mutation (M45V) in CEM/S20 cells, salinosporamide A displayed a markedly impaired capacity to inhibit beta(5)-associated catalytic activity. Last, compared with parental CEM cells, CEM/S20 cells exhibited up to 2.5-fold upregulation of constitutive proteasome subunits, while retaining unaltered immunoproteasome subunit expression. In conclusion, salinosporamide A displayed potent antileukemic activity against bortezomib-resistant leukemia cells. beta-Subunit point mutations as a common feature of acquired resistance to salinosporamide A and bortezomib in hematologic cells and S. tropica suggest an evolutionarily conservedmechanism of resistance to proteasome inhibitors.

Moore, BS.  2018.  Asymmetric Alkene and Arene Halofunctionalization Reactions in Meroterpenoid Biosynthesis. Synlett. 29:401-409.   10.1055/s-0036-1590919   AbstractWebsite

Meroterpenoid natural products are important bioactive molecules with broad distribution throughout nature. In Streptomyces bacteria, naphthoquinone-based meroterpenoids comprise a simple yet structurally fascinating group of natural product antibiotics that are enzymatically constructed through a series of asymmetric alkene and arene halofunctionalization reactions. This account article highlights our discovery and characterization of a group of vanadium-dependent chloroperoxidase enzymes that catalyze halogen-assisted cyclization and rearrangement reactions and have inspired biomimetic syntheses of numerous meroterpenoid natural products. 1 Introduction 2 Early Biosynthetic Insights and the Characterization of Alkene Halofunctionalization in Napyradiomycin Biosynthesis 3 Discovery of the Merochlorin Natural Products and Enzymatic Aryl Halofunctionalization 4 Discovery and Development of Unifying THN-Based Meroterpenoid Biosynthesis and Synthesis Approaches 5 Insights into Naphterpin and Marinone Biosynthesis Involving Cryptic Aryl Halofunctionalization Reactions 6 Closing Thoughts

Mohimani, H, Kersten RD, Liu WT, Wang MX, Purvine SO, Wu S, Brewer HM, Pasa-Tolic L, Bandeira N, Moore BS, Pevzner PA, Dorrestein PC.  2014.  Automated genome mining of ribosomal peptide natural products. Acs Chemical Biology. 9:1545-1551.   10.1021/cb500199h   AbstractWebsite

Ribosomally synthesized and posttranslationally modified peptides (RiPPs), especially from microbial sources, are a large group of bioactive natural products that are a promising source of new (bio)chemistry and bioactivity.(1) In light of exponentially increasing microbial genome databases and improved mass spectrometry (MS)-based metabolornic platforms, there is a need for computational tools that connect natural product genotypes predicted from microbial genome sequences with their corresponding chemotypes from metabolomic data sets. Here, we introduce RiPPquest, a tandem mass spectrometry database search tool for identification of microbial RiPPs, and apply it to lanthipeptide discovery. RiPPquest uses genomics to limit search space to the vicinity of RiPP biosynthetic genes and proteomics to analyze extensive peptide modifications and compute p-values of peptide-spectrum matches (PSMs). We highlight RiPPquest by connecting multiple RiPPs from extracts of Streptomyces to their gene clusters and by the discovery of a new class III lanthipeptide, informatipeptin, from Streptomyces viridochromogenes DSM 40736 to reflect that was discovered by mass spectrometry based genome mining using algorithmic tools rather than manual inspection of mass spectrometry data and genetic information. The presented tool is available at cyclo.ucsd.edu.

Xu, Y, Kersten RD, Nam SJ, Lu L, Al-Suwailem AM, Zheng HJ, Fenical W, Dorrestein PC, Moore BS, Qian PY.  2012.  Bacterial Biosynthesis and Maturation of the Didemnin Anti-cancer Agents. Journal of the American Chemical Society. 134:8625-8632.   10.1021/ja301735a   AbstractWebsite

The anti-neoplastic agent didemnin B from the Caribbean tunicate Trididemnum solidum was the first marine drug to be clinically tested in humans. Because of its limited supply and its complex cyclic depsipeptide structure, considerable challenges were encountered during didemnin B's development that continue to limit aplidine (dehydrodidemnin B), which is currently being evaluated in numerous clinical trials. Herein we show that the didemnins are bacterial products produced by the marine alpha-proteobacteria Tistrella mobilis and Tistrella bauzanensis via a unique post-assembly line maturation process. Complete genome sequence analysis of the 6,513,401 bp T. mobilis strain KA081020-065 with its five circular replicons revealed the putative didemnin biosynthetic gene cluster (did) on the 1,126,962 bp megaplasmid pTM3. The did locus encodes a 13-module hybrid non-ribosomal peptide synthetase-polyketide synthase enzyme complex organized in a collinear arrangement for the synthesis of the fatty acylglutamine ester derivatives didemnins X and Y rather than didemnin B as first anticipated. Imaging mass spectrometry of T. mobilis bacterial colonies captured the time-dependent extracellular conversion of the didemnin X and Y precursors to didemnin B, in support of an unusual post-synthetase activation mechanism. Significantly, the discovery of the didemnin biosynthetic gene cluster may provide a long-term solution to the supply problem that presently hinders this group of marine natural products and pave the way for the genetic engineering of new didemnin congeners.

Harvey, EL, Deering RW, Rowley DC, Elgamal A, Schorn M, Moore BS, Johnson MD, Mincer TJ, Whalen KE.  2016.  A bacterial quorum-sensing precursor induces mortality in the marine coccolithophore, Emiliania huxleyi. Frontiers in Microbiology. 7   10.3389/fmicb.2016.00059   AbstractWebsite

Interactions between phytoplankton and bacteria play a central role in mediating biogeochemical cycling and food web structure in the ocean. However, deciphering the chemical drivers of these interspecies interactions remains challenging. Here, we report the isolation of 2-heptyl-4-quinolone (HHQ), released by Pseudoalteromonas piscicida, a marine gamma-proteobacteria previously reported to induce phytoplankton mortality through a hitherto unknown algicidal mechanism. HHQ functions as both an antibiotic and a bacterial signaling molecule in cell cell communication in clinical infection models. Co -culture of the bloom -forming coccolithophore, Emiliania huxleyi with both live P piscicida and cell -free filtrates caused a significant decrease in algal growth. Investigations of the P piscicida exometabolome revealed HHQ, at nanomolar concentrations, induced mortality in three strains of E. huxleyi. Mortality of E. huxleyi in response to HHQ occurred slowly, implying static growth rather than a singular loss event (e.g., rapid cell lysis). In contrast, the marine chlorophyte, Dunaliella tertiolecta and diatom, Phaeodactylum tricornutum were unaffected by HHQ exposures. These results suggest that HHQ mediates the type of inter -domain interactions that cause shifts in phytoplankton population dynamics. These chemically

Kale, AJ, McGlinchey RP, Lechner A, Moore BS.  2011.  Bacterial Self-Resistance to the Natural Proteasome Inhibitor Salinosporamide A. Acs Chemical Biology. 6:1257-1264.   10.1021/cb2002544   AbstractWebsite

Proteasome inhibitors have recently emerged as a therapeutic strategy in cancer chemotherapy, but susceptibility to drug resistance limits their. efficacy. The marine actinobacterium Salinispora tropica produces salinosporamide A (NPI-0052, marizomib), a potent proteasome inhibitor and promising clinical agent in the treatment of multiple myeloma. Actinobacteria also possess 20S proteasome machinery, raising the question of self resistance We identified a redundant proteasome beta-subunit, SalI, encoded within the salinosporamide biosynthetic gene cluster and biochemically characterized the Sall proteasome complex. The SalI beta-subunit has an altered substrate specificity profile, 30-fold resistance to salinosporamide A, and cross resistance to the FDA approved proteasome inhibitor bortezomib. An A49V mutation in Sall correlates to clinical bortezomib resistance from a human proteasome beta 5-subunit A49T mutation, suggesting that intrinsic resistance to natural proteasome inhibitors may predict clinical outcomes.

Wilson, MC, Moore BS.  2012.  Beyond ethylmalonyl-CoA: The functional role of crotonyl-CoA carboxylase/reductase homologs in expanding polyketide diversity. Natural Product Reports. 29:72-86.   10.1039/c1np00082a   AbstractWebsite

This review covers the emerging biosynthetic role of crotonyl-CoA carboxylase/ reductase (CCR) homologs in extending the structural and functional diversity of polyketide natural products. CCRs catalyze the reductive carboxylation of alpha,beta-unsaturated acyl-CoA substrates to produce a variety of substituted malonyl-CoA derivatives employed as polyketide synthase extender units. Here we discuss the history of CCRs in both primary and secondary metabolism, the mechanism by which they function, examples of new polyketide diversity from pathway specific CCRs, and the role of CCRs in facilitating the bioengineering novel polyketides.

Zhao, B, Guengerich FP, Bellamine A, Lamb DC, Izumikawa M, Lei L, Podust LM, Sundaramoorthy M, Kalaitzis JA, Reddy LM, Kelly SL, Moore BS, Stec D, Voehler M, Falck JR, Shimada T, Waterman MR.  2005.  Binding of two flaviolin substrate molecules, oxidative coupling, and crystal structure of Streptomyces coelicolor A3(2) cytochrome P450 158A2. Journal of Biological Chemistry. 280:11599-11607.   10.1074/jbc.M410933200   AbstractWebsite

Cytochrome P450 158A2 ( CYP158A2) is encoded within a three-gene operon ( sco1206-sco1208) in the prototypic soil bacterium Streptomyces coelicolor A3( 2). This operon is widely conserved among streptomycetes. CYP158A2 has been suggested to produce polymers of flaviolin, a pigment that may protect microbes from UV radiation, in combination with the adjacent rppA gene, which encodes the type III polyketide synthase, 1,3,6,8-tetrahydroxynaphthalene synthase. Following cloning, expression, and purification of this cytochrome P450, we have shown that it can produce dimer and trimer products from the substrate flaviolin and that the structures of two of the dimeric products were established using mass spectrometry and multiple NMR methods. A comparison of the x-ray structures of ligand-free (1.75 angstrom ) and flaviolin-bound (1.62 angstrom) forms of CYP158A2 demonstrates a major conformational change upon ligand binding that closes the entry into the active site, partly due to repositioning of the F and G helices. Particularly interesting is the presence of two molecules of flaviolin in the closed active site. The flaviolin molecules form a quasi-planar three-molecule stack including the heme of CYP158A2, suggesting that oxidative C-C coupling of these phenolic molecules leads to the production of flaviolin dimers.

Kersten, RD, Lane AL, Nett M, Richter TKS, Duggan BM, Dorrestein PC, Moore BS.  2013.  Bioactivity-Guided Genome Mining Reveals the Lomaiviticin Biosynthetic Gene Cluster in Salinispora tropica. ChemBioChem. 14:955-962.: WILEY-VCH Verlag   10.1002/cbic.201300147   AbstractWebsite

The use of genome sequences has become routine in guiding the discovery and identification of microbial natural products and their biosynthetic pathways. In silico prediction of molecular features, such as metabolic building blocks, physico-chemical properties or biological functions, from orphan gene clusters has opened up the characterization of many new chemo- and genotypes in genome mining approaches. Here, we guided our genome mining of two predicted enediyne pathways in Salinispora tropica CNB-440 by a DNA interference bioassay to isolate DNA-targeting enediyne polyketides. An organic extract of S. tropica showed DNA-interference activity that surprisingly was not abolished in genetic mutants of the targeted enediyne pathways, ST_pks1 and spo. Instead we showed that the product of the orphan type II polyketide synthase pathway, ST_pks2, is solely responsible for the DNA-interfering activity of the parent strain. Subsequent comparative metabolic profiling revealed the lomaiviticins, glycosylated diazofluorene polyketides, as the ST_pks2 products. This study marks the first report of the 59 open reading frame lomaiviticin gene cluster (lom) and supports the biochemical logic of their dimeric construction through a pathway related to the kinamycin monomer.

Xiang, LK, Moore BS.  2005.  Biochemical characterization of a prokaryotic phenylalanine ammonia lyase. Journal of Bacteriology. 187:4286-4289.   10.1128/jb.187.12.4286-4289.2005   AbstractWebsite

The committed biosynthetic reaction to benzoyl-coenzyme A in the marine bacterium "Streptomyces maritimus" is carried out by the novel prokaryotic phenylalanine ammonia lyase (PAL) EncP, which converts the primary amino acid L-phenylalanine to trans-cinnamic acid. Recombinant EncP is specific for L-phenylalanine and shares many biochemical features with eukaryotic PALs, which are substantially larger proteins by 200 amino acid residues.

Teufel, R, Stull F, Meehan MJ, Michaudel Q, Dorrestein PC, Palfey B, Moore BS.  2015.  Biochemical establishment and characterization of EncM's flavin-N5-oxide cofactor. Journal of the American Chemical Society. 137:8078-8085.   10.1021/jacs.5b03983   AbstractWebsite

The ubiquitous flavin-dependent monooxygenases commonly catalyze oxygenation reactions by means of a transient C4a-peroxyflavin. A recent study, however, suggested an unprecedented flavin-oxygenating species, proposed as the flavin-N5-oxide (Fl(N5[O])), as key to an oxidative Favorskii-type rearrangement in the biosynthesis of the bacterial polyketide antibiotic enterocin. This stable superoxidized flavin is covalently tethered to the enzyme EncM and converted into FADH(2) (Fl(red)) during substrate turnover. Subsequent reaction of Flred with molecular oxygen restores the postulated Fl(N5[O]) via an unknown pathway. Here, we provide direct evidence for the Fl(N5[O]) species via isotope labeling, proteolytic digestion, and high-resolution tandem mass spectrometry of EncM. We propose that formation of this species occurs by hydrogen-transfer from Fl(red) to molecular oxygen, allowing radical coupling of the formed protonated superoxide and anionic flavin semiquinone at N5, before elimination of water affords the Fl(N5[O]) cofactor. Further biochemical and spectroscopic investigations reveal important features of the Fl(N5[O]) species and the EncM catalytic mechanism. We speculate that flavin-N5-oxides may be intermediates or catalytically active species in other flavoproteins that form the anionic semiquinone and promote access of oxygen to N5.

Moore, BS, Hertweck C.  2002.  Biosynthesis and attachment of novel bacterial polyketide synthase starter units. Natural Product Reports. 19:70-99.   10.1039/b003939j   AbstractWebsite

The biosynthesis and mode of attachment of a wide range of polyketide synthase (PKS) starter units in bacteria are covered in this review. Natural, unnatural, and engineered starter units associated with type I and type II PKSs are reported. The literature through early 2001 is reviewed, and 240 references cited.

Kalaitzis, JA, Hamano Y, Nilsen G, Moore BS.  2003.  Biosynthesis and structural revision of neomarinone. Organic Letters. 5:4449-4452.   10.1021/ol035748b   AbstractWebsite

The biosynthesis of the meroterpenoid neomarinone from a marine actinomycete was probed through feeding experiments with C-13-labeled precursors. NMR characterization of [U-C-13(6)]glucose-enriched neomarinone led to the structural revision of structure 4a to 4b, which was confirmed by extensive 2D NMR spectrometry with unlabeled compound.