[S,D] Introduction to Sociology
[S,D] Introduction to Sociology Soc 101
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Date Created: 09/17/15
REPORTS precursors containing simple alkyl esters un derwent Michael addition but the resulting adducts did not cyclize Perhaps even marka le than the condensation that produces 21 is the parallel transformation 0 with the enone 4 Fig 3 entry 1 which forms 6 deoxytetracycline 6 in protected form wi gt 1 iastereoselectivity in 81 yield a er puri cation by RP HPLC diastereomer ica y pure a minor diastereomer epimeric a C6 was also isolated separately It appears that additions to 4 and 5 proceed almost exclusively by addition to one face of each enone the top face as drawn in Fig 1B producing CSa stereochemistry corresponding to that of natural tetracyclines although why this should be the case is not obvious we prepared six 6 deoxytetracyclin Fig 3 In each case it was necessary to op timize the speci c conditions for 0toluate anion generation and trapping For the synthe sis of products 8 9 and 10 Fig 3 anion generation was best conducted in situ in the presence of the enone 4 either by selective deprotonation 8 or by lithium halogen ex change 9 and 10 A number of potentially competing nonproductive reaction sequences might have intervened during 39 39 anion generation such as enolization of 4 the ob served efficiencies ofthe transformations are surprising in light of this It is also note wo y that in situ anion generation permits the use of atoluates lacking an 0 koxy substituent such as used in the synthesis of 8 and 9 substrates that are known to be problematic from prior studies 35 Also li ium halogen exchange reactions of ben zylic halides such as used in the synthesis of 9 had previously been considered impracticable 36 37 The e iciencies of the synthetic sequences analog for antibacterial testing using stan dard serial dilution techniques in 5 to 20 mg amounts Minimum inhibitory concentrations MICs were determined for each analog in whole cell antimicrobial assays using five 39 39 f am negative or 3 Thus far the pentacycline derivative 10 has shown the most promising antibacterial properties with activity equal to or greater tetracycline in each of the Gram positive strains examined including strains 39th resistance to te acycline methicil in and vancomycin Although this nding is note worthy it is very likely that antibiotics with even greater potencies andor improved pharmacological properties will emerge with er explora ion of e complex chemical space now made accessible by the versatile synthetic route described 398 References and Notes 1 C Walsh Antibiotics Actions Origins Resistance American Society for Microbiology Press Washing ton DC 2003 2 s c Amyes Magic Bullets Lost Horizons the Rise and Fall ofAntibiotics Taylor and Francis New Vork 2001 M Leeb Nature 431 892 2004 w R Strohl Metab Eng 3 4 2001 D E Cane C T Walsh C Khosla Sc39 nce 282 63 1998 L Katz Chem Rev 97 2557 1997 c R Stephens et a j Am Chem Soc 85 2543 1963 M Nelson W Hillen R A Greenwald Eds Tetracyclines in Biology chemistry and Medicine Birkhauser Verlag Boston 2001 D E Brodersen et a Cell 103 1143 2000 10 M Pioletti et a EMBO j 20 1829 2001 11 PE Sum P Petersen Bioorg Med Chem Lett 9 1459 1999 12 K Bush M Macielag M WeidnerWells Curr Opin Microbiol 7 455 2004 i Korst etal Am Chem Soc 90 439 1968 A i Gurevich et a Tetrahedron Lett 8 131 1967 H Muxfeldt eta Am Chem Soc 101 689 1979 K Talsuta T Voshimoto H Gunji V Okado M Takahashi Chem Lett jpn 2000 545 2000 17 c Stork i La Clair P Spar o R P Nargund N Totah j Am Chem Soc 118 5304 1996 w Rogalski in Handbook of Experimental Pharma cology Hlavka H Boothe Eds Springer Verlag New York 1985 vol 78 cha 5 19 A M Reiner G D Hegeman Biochemistry 10 2530 1971 20 A G Myers D R Siegel D J Buzard M G Charest Org Lett 3 2923 2001 21 G Stork A A Hagedorn Hi j Am Chem Soc 100 3509 1978 22 D M V as V Chiang T W Doyle Tetrahedron Lett 25 487 1984 23 P Pevarello M Varasi Synth Commun 22 1939 1992 4 S H Pine Org React 18 403 1970 25 G Myers B Zheng Tetrahedron Lett 37 4841 1996 W QMPW ED pitabu no N 25 M Frigerio M Santagostino Tetrahedron Lett 35 8019 1994 7 E Corey H Cho c Rucker D H Hua Tetrahedron Lett 22 3455 1981 28 F A Davis M c Weismiller c K Murphy R T Reddy BC Chen j Org Chem 57 7274 1992 E N Prilezhaeva Russ Chem Rev 70 897 2001 TL Ho Tandem Organic Reactions Wiley New York 1992 31 F Leeper Staunton j Chem Soc Chem Comm 1978 405 1978 2 M Hauser R P Rhee j Org Chem 43 178 1978 33 i H Dodd 5 M Weinreb Tetrahedron Lett 20 3593 1979 N wN om 34 i D white E c Nolen r c H Miller Org Chem 5111501986 F M Hauser R P Rhee s Prasanna s M Weinreb H Dodd Synthesis Mass 1980 72 1980 35 w E Parham L D ones v A Sayed j Org Chem 37 s c Berk M P Veh N eong P Knochel Organornetaiiics 9 3053 1990 38 We thank D Kahne and c Wa 1 for helpful discussions and w Brubaker Farmington Pharma Development and r Thoma and Thanass39 Achillion Pharmacue ticais for antibacterial screening is work was supported by NiH grant Al48825 NSF predoctoral graduate fellowships MGC and me and the kademischer Austausch Dienst CDL is a consultant for P zer The research described here is independent Supporting Online Material wwwsciencemagorgcgicontentfull3085720395 DC1 Materials and Methods References 13 anuary 2005 accepted 1 March 2005 101126science1109755 Hypoxia Global Warming and Terrestrial Late Permian Extinctions Raymond B Hueyquot and Peter D Ward A catastrophic extinction occurred at the end of the Permian Period However baseline extinction rates appear to have been elevated even before the final catastrophe suggesting sustained environmental degradation For terrestrial vertebrates during the Late Pennian the combination of a drop in atmospheric oxygen plus climate warming would have induced hypoxic stress and consequently compressed altitudinal ranges to near sea level Our simulations suggest that the magnitude of altitudinal compression would have forced extinctions by reducing habitat diversity fragmenting and isolating populations and inducing a speciesarea ef recovew after the mass extinction A catastrophic extinction marks the end of the Permian 1 2 and is attributed to an acute climate crisis among other causes 3 5 How er b ckground extinction rates and ecosystem turnover were elevated throughout much of the Late Permian 6 7 and recovery a er extinction was slow 1 2 T us en vironmenta egra tion likely occurred bo before and after the final catastrophe perhaps caused by major shifts in atmospheric chem istry 8 Indeed modeling isotope and fect It also might have delayed ecosystem paleontological evidence 9 13 suggests that 02 levels plummeted in the Late Permian an re 1cted the same time CO2 levels were rising Fig 1A and climate warming 14 would have increased metabolic demand for 02 Severe hypoxia was inevitable 9 15 16 Here we explore a biogeographic conse quence of presumed low 0 levels during the Late Permian and Triassic Terrestrial animals 15APRL 2005 VOL308 SCIENCE wwwsciencemagorg 400 REPORTS plus warm water temperatures would lower aquatic 02 levels but warm body temper atures increase 02 demand Thus water breathing ectotherms would likely have been 02 challenged even near sea level Insects which su ered major extinctions during the Late Permian 23 might also have experienced some hypoxia and altitudinal compression Insect development is slowed by low PO2 plus warm temperatures 24 Inter estingly giant dragon ies which evolved during the Permian 02 high are thought to have gone extinct in the Late Permian because of limitations on O2 diffusion 9 However today s large adult insects rely on convec tive ventilation and are remarkably hypoxia tolerant 25 thus the aquatic larvae of giant insects may have been the primary targets of hypoxia induced extinction Altitudinal compression would have had important biogeographic consequences Ani mals specialized for upland habitats could not have survived as they would have been physiologically excluded from them More over mountain passes would have seemed physiologically higher to animals 26 than are passes of equivalent altitude today Thus populations would have become fragmented and isolated fig S2 and rates of local extinction may have increased 2 7 Altitudinal compression plus rising sea levels at the very end of the Permian I4 28 would have also reduced the land surface physiologically accessible to animals This loss would have caused additional extinctions via a species area effect 29 and also would have delayed the recovery Topographic maps for the mid Permian to Late Permian 30 enable us to estimate 20 albeit with substantial uncertainty the per centage of the land surface that was physio logically accessible to animals with specified hypoxia tolerance Fig 2 During the 02 high in the Permian virtually the entire surface of Earth had sufficient O2 to sustain populations of our hypothetical species By the Triassic however hypoxia would have reduced acces Fig 2 Plot of cumulative land area 100 versus physical altitude during the mid Permian to Late Permian solid line 30 and for the present day dashed line 20 This relationship enables us to estimate the per centage of the land surface that was physiologically tolerable 20 for the hypothetical species shown in Fig 1C A species capable of surviving up to 60 km in the mid Permian would been restricted to 20 below 03 km by the end of the Permian gray dotted line and thus would have been able to 07 Cumulative area sible land area for all but the most hypoxia tolerant species Fig 1C For example a species physiologically capable of surviving up to 60 km in the mid Permian would have been restricted to below 03 km by the Triassic thus it would have been excluded from more than half of the available land surface gray dotted line in Fig 2 By the early Triassic Fig 1A even a species that could tolerate 80 km in the mid Permian would have likely gone extinct Fig 1C in the absence of compensatory adaptation Thus altitudinal compression could have had sub stantial effects on extinction and recovery rates given the huge loss in land for all but the most hypoxia resistant taxa Fig 2 The reasonableness of our scenario of hypoxia induced altitudinal compression de pends fundamentally on the accuracy and timing of estimates of percent 02 8 Those estimates of course have uncertainty 8 20 and other models can yield somewhat differ ent estimates 2 3 Our analyses also assume that 02 restricted the upper altitudinal limits during the Late Permian and Triassic that terrestrial verte brates then had modest hypoxia tolerance and that adaptation to hypoxia was limited None of these assumptions can be directly tested as yet but our compression hypothesis leads to predictions and patterns that are subject to test 1 Terrestrial vertebrates that did survive the Late Permian should show respiratory adaptations for hypoxia Indeed morphologi cal traits of Lystrosaums one of the few surviving therapsids and of other Triassic dicynodonts have been interpreted as adapta tions to hypoxia 6 3l 2 Hyperventilation in response to hypoxia would have elevated respiratory water loss during the Late Permian Maxilloturbinates which reduce respiratory water loss first evolved at that time in mammal like reptiles 32 Turbinates have been interpreted as in dicating high respiratory rates associated with endothermy 32 but they might also be midlate Permian quot present day occupy less than half of the 0 available land area Less hypoxia tolerant species would have gone 10 20 30 Physical altitude km extinct more tolerant ones would have suffered minimal area loss indicators of high respiratory rates induced by hypoxia 3 Fossil sites for terrestrial ectotherms by the Triassic should be located predominantly at high latitude where relatively cooler temperatures would reduce metabolic require ments for O2 and ameliorate hypoxia Distri butional data for therapsids are consistent 33 However therapsids might also have been restricted to high latitude simply because low latitude sites were hot dry and had a depauperate ora 34 4 The compression forced isolation of taxa into refugia could help to explain Late Permian endemism 33 which is surprising for a Pangaean supercontinent It could also help to explain the Lazarus effect ie the reappearance of taxa that disappeared from the fossil record noted in this period I 35 The extinctions during the Late Permian were the largest ever during the history of life on Earth An abrupt climate change is thought to be responsible for the catastrophic extinc tion Nonetheless hypoxia may have contrib uted to the high background extinctions and high faunal turnover occurring before the mass extinction to the final catastrophe itself and to the delayed recovery Low 02 levels would have promoted extinction and delayed recovery directly via physiological stress 16 and indirectly via altitudinal compression Note added in proof A forthcoming paper 36 provides new and fine scaled estimates of 02 levels during the Late Permian and Early Triassic The drop in 02 during the Late Permian is slightly more recent than that in Fig 1A but still suggests that hypoxia and altitudinal compression were influential both before and after the mass extinction References and Notes D H Erwin The Great Paleozoic Crisis Columbia Univ Press New York 1993 S A Bowring D H Erwin Y lsozaki Proc Natl Acad Sci USA 96 8827 1999 A H Knoll R K Bambach D E Canfield J P Grotzinger Science 273 452 1996 4 R A Berner Proc Natl Acad Sci USA 99 4172 N UJ 2002 5 M J Benton R J Twichett Trends Ecol Evol 18 358 2003 6 M J Benton V P Tverdokhlebov M V Surkov Nature 432 97 2004 P D Ward et al Science 307 709 2005 published online 20 January 2005 101126science1107068 R A Berner Geochim Cosmochim Acta 65685 2001 J B Graham R Dudley N Aguilar C Gans Nature 375 117 1995 A C Lasaga H Ohmoto Geochim Cosmochim Acta 66 361 2002 N D Sheldon G J Retallack Geology 30 919 2002 N M Bergman T M Lenton A J WatsonAm 1 Sci 304 397 2004 R A Berner The Phanerozoic Carbon Cycle C02 and 02 Oxford Univ Press Oxford 2004 D L Kidder T R Worsley Palaeogeogr Palaeoclimatol Palaeoecol 203 207 2004 15 R A Berner D J Beerling R Dudley J M Robinson R A Wildman Jr Annu Rev Earth Planet Sci 31 105 2003 G J Retallack R M H Smith P D Ward Geol Soc Am Bull 115 1133 2003 N 599 O UJ N l 1 gt OH 15 APRIL 2005 VOL 308 SCIENCE www5ciencemagorg 17 P Bouverot Adaptation to Altitude Hypoxia in Vertebrates SpringerVerlag Berlin 1985 1 K i Gaston The Stnicture and Dynamics of Geographic Ranges Oxford Univ Press Oxford 2003 19 We estimate PiOZ rat er than P02 because the additi n of respiratory water vapor reduces the partial pressure of O2 in the lung 20 20 See su rting data on Science Online 21 Estimates of maximum altitudes for the Late Permian and Triassic are somewhat low because warm temperatures would have elevated barometric pres sure at altitu e However the im act on O2 would been small Substituting POZ and temperature estimates in the hypsometric equation demonstrates that our altitudinal estimates for the Triassic OZ low Fig 1c underestimate actual limits by at most 01 km 22 Similarly our estimates of maximum altitudes in the old midPermian Fig 1c overestimate actual limits by at most 02 km 22 Because these effects are relatively small we ignore the m in our simulations 22 D Battisti personal communication c c Labandeira l l Sepkoski lr Science 251 310 1993 M R Frazier H A Woods 1 F Harrison Physiol Biochem Zool 74 541 2001 25 K i Greenlee i F Harrison j Exp Biol 207 497 2004 25 D H lanzen Am Nat 101 233 1957 27 l A Hanski Metapopulation Ecology Oxford Univ Press Oxford 1999 28 A Hallam P B Wignall Eaitir Sci Rev 43 217 1999 29 M L Rosenzweig Species Diversity in Space and Time Cambridge Univ Press Cambridge 1995 30 D B Rowley R T Pierrehumbert B S Currie Earth Planet Sci Lett 1313 253 2001 31 K Ang39elczyk personal communication 32 W l Hillenius l A Ruben Physiol Biochem Zool 4 33 c A Sidor et al Natuie in press 34 P M Rees Geology 30 827 2002 35 P B Wignall M 1 Benton j Geol Soc London 155 453 1999 35 R A Berner Geochim Cosmochim Acta in press OpenSystem Coral Ages Reveal Persistent Suborbital SeaLevel Cycles William C Thompsonquot and Steven L Goldstein Sea level is a sensitive index of global climate that has been linked to Earth s orbital variations with a minimum periodicity of about 21000 years Although there is ample evidence for climate oscillations that are too frequent to be explained by orbital forcing suborbitalfrequency sealevel change has been difficult to resolve primarily because of problems with uraniumthorium coral dating Here we use a new approadi that corrects coral ages for the frequently observed opensystem behavior of uraniumseries nuclides substantially improving the resolution of sealevel reconstruction This curve reveals persistent sealevel oscillations that are too frequent to be explained ex clusively by orbital forcing The idea that Quaternary climate cycles are linked to changes in Earth s orbit is central to the marine oxygen isotope 5130 record 2 and early dating of coral terraces 3 However there is abun t evidence for abrupt climate change that was too frequent to be explained by orbital changes 4 Here we attempt to reconstruct sea level between 70 and 240 thousand years ago ka with a resolution sufficient to detect suborbital frequency oscillations using a new approach to UTh coral dating 5 Sev eral recent lines of evidence suggest that sea level may be more variable than previously thought An example is the conversion via a hydraulic model of a salinity record from the Red Sea into a sea level curve for the past 470 Lamont Doherty Earth Observatoly LDEO and Department of Earth and Environmental Sciences Columbia University Palisades NY 10964 USA Present address Department of Geology and Geo physics 118 Clark Lab Mail Stop 23 Woods Hole Oceanographic Institution Woods Hole MA 02543 USA TTowhom correspondence should be addressed E mail wthompsonwhoie u www5ciencemagorg SCIENCE VOL308 thousand years ky 6 This record suggests fairly large 35 m suborbital frequency sea level changes during glacial periods such as marine iso ope stage more mod est 15 m changes during interglacials for example during MIS 5 This new Red Sea record augments a growing body of evidence for suborbital sea level uctuations in coral records At the Huon Peninsula of Papua New Guinea multiple coral terraces were formed during MIS 3 with highstands occurring about every 6 ky 7 8 There are also more Huon terraces associated with MIS 5 than can be accounted for by orbital variability 9 Such evidence is not restricted to New Guinea closely spaced terraces on Barbados suggest suborbital period changes in sea level during MIS 5a and MIS 5c 9 10 e construction of a high resolution sea level record requires a large number of a curate coral ages from a limited geographic area and this has not been possible with ndar methods The conventional equations for UTh age determination 1 require that loss or gain of an have not occurred except by radioactive decay a er coral death This closed system requirement 15 APRIL 2005 REPORTS 37 R A Berner Z KoihavalaAM j Sci 301 182 2001 R Berner for providing data advice and discussion K Angielczyk M Be ton Buick C Carey T Daniel R Dudley D Erwin 1 Graham T Hornbein D Rowley j Ruben A Smith M Stoeck West for discussion D Battisti for computing mperature on critical altitudes and G Wang for calculating hypsometric data Supported by NSF grant IBN0416843 RBH and the NASA Astrobiology lnstitute University of Washington Node PDW principal investigator and 1 Supporting Online Material www5ciencemagorgcgicontentfull3085720398 DC I Materials and Methods Figs S1 and S2 References 29 November 2004 accepted 15 February 2005 IO I126science1108019 is often violated in fossil corals as a result of e alpha recoil mobili of U series nuclides 12 and an initial coral 234U23 3U ratio that is significantly different from that of modern seawater is taken as evidence of open system behavior and an unreliable age 13 Building n earlier attempts to correct for open system behavior 14 we have derived a set of decay equations that corrects coral ages for these effects 5 Although conventional U series cora ages from a single stratigraphic level o en differ substantially open system ages of these corals are in much etter agreement Fig 1 A to C which illustrates the dra matic improvement in the accuracy of coral ages achieved through open system dating It has long been known that many conven tional coral ages are unreliable prompting screening for open system effects 13 Such screening improves accuracy but o en results in the rejection of up to 90 of measured ages degra ing the resolution of sea level reconstructions fig S1 B y re covering accurate ages for most corals the open system method greatly improves the res olution of the resulting record fig S1C have constructed 15 a high resolut uplift corrected sea level curve for Barba Fig 2 with o en system ages calculated from published isotope ratio data 5 13 16 17 and other measurements table S1 Corals defining this curve are almost entirely Acrapam palmta a reef crest species An average data density approaching one age per 1000 years during MIS 5 highstands and one age per 2500 years during MIS 7 to 220 ka resolves sea level uctuations occurring over a few ion 0 ons define the oscillations characterizing subor ital sea level variability However in mid MIS 7 between 200 and 220 ka three potential sea level peaks are poorly resolved because of overlapping error envelopes T e best con strained portion of the sea level curve is during MIS 5c where minor highstands at 100 103 and 1055 ka are evident in coral ages from a 401
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