Module #4 - Antibiotics Flashcards
what are antibiotics
anti life
contain poisons that selectively target microbes like bacteria, fungi, protozoa and viruses
who came up with magic bullet, tarpan red, and Salvarsan 606
Paul erlich
magic bullet concept
describes idea of something being able to selectively kill microbes within body without harming body itself
like firing gun at a specific target
trypan red discovery
Erlich noticed some cells under microscope took in red dye more than others and discovered some chemical property was causing this
trypanosome cells were studies (sleeping sickness)
describe Salvarsan 606 discovery/SAR
Erlich used structure of red dye, but replaced nitrogen with arsenic to develop poison that targeted bad cells only
characteristics + issues of Salvarsan 606
target syphillis
1st antibiotic to be sold
issues = insoluble, large doses through injection (no iv therefore caused necrosis)
who is responsible for creation of prontosil? three general characteristics
Gerhard domagk
1st commercially successful antibiotic, made from another chemical dye, only effective in-vivo (liver) because it is where active form is made
what is the active form of prontosil? how is it formed?
sulfanilamade
prontosil enters liver - metabolism takes place - prontosil essentially cut in half - sulphanilamide formed (active form)
main purposes of sulfanilamide + why is it important to have strong immune system
prevents the production of coenzyme F which inhibits bacterial growth
good immune system required because it kills off any remaining bacteria
how is coenzyme F produced? what does its production allow for?
PABA is the messenger molecule for the enzyme that produces coenzyme F
PABA binds to active site of enzyme which in turn produces coenzyme F
production allows for bacterial growth to occur
how does sulfanilamide prevent the production of coenzyme F? what type of inhibition takes place?
acts as a competitive inhibitor
resembles PABA, and binds to active site of enzyme that produces coenzyme F
interacts with/blocks active site so PABA can no longer bind
therefore, not coenzyme F production
why does protosil/sulfanilamide not harm the human body?
human body lacks coenzyme F
therefore there is nothing in the human body that sulfanilmade can interact with
what part of drug is typically modified when SAR is performed?
heterocycle - the part of the molecule that doesn’t make it into the active site of an enzyme
most penicillins are _____. what does this term mean?
semi-synthetic (modified versions of natural penicillin)
are more drug-like than the original penicillin
describe the discoveries of Alexander fleming
accidentally contaminated Petri dish of bacteria with some mold growing in this lab
mold was unknowingly penicillin mold that secreted penicillin
penicillin killed some of bacteria in the dish
didn’t realize the discovery he had made, but published findings
describe the discoveries of Howard Florey and Ernest Chain
spent years trying to determine the chemical substance tat the mold in Fleming’s lab was secreting - and succeeded
published data showing that penicillin could kill disease w/o harming the organism
describe the structure of human cells
surrounded by cell membrane
no cell wall
inner contents exist at low pressure
describe the structure of bacterial cells
surrounded by cell membrane and cell wall
inner content exist at high pressure
importance of bacterial cell wall
protects cell from outside environment and contains the high internal osmotic pressure
is rigid, imparts structure, and resists the pressure
also the target of penicillin
what causes cellular osmotic pressure
lots of stuff inside cells, and less outside = results in conc. gradient
conc gradient balanced by moving solvent through membrane = results in osmotic pressure
describe overall structure of cell wall
peptidoglycan structure
consists of polysaccharide chains (sugar chains) and peptide cross links (amino acids) that connect the polysaccharide chains together
what does a larger peptidoglycan structure result in?
stronger cell wall therefore greater ability of bacteria cell to withstand osmotic pressure
how do polysaccharide chains and peptide cross links relate?
polysaccharide chains very weak/slippery
cross links form connections between strands creating a rigid network
what is transpeptidase
the enzyme that links together peptide chains to form peptide cross links in the peptidoglycan structure of bacterial cell walls
what is the difference between L and D amino acids?
both represent overall structure/configuration/stereochemistry of amino acids
L = very common
D = very rare, but seen in peptide chains/cross links
only difference is stereochemistry of side chain = R group is wedge in D, and hash in L
how is a peptide cross link formed?
transpeptidase enzyme links together peptide chains to form peptide cross links
what is the main purpose of penicillin?
to block transpeptidase enzyme
this means that peptide cross links can no longer be formed, resulting in weak cell wall
wall will not be able to withstand strong osmotic pressure, and cell will eventually blow up
what does transpeptidase recognize as substrate?
D-Ala
what peptide structure does penicillin resemble?
D-Ala-D-Ala
what family is transpeptidase enzyme a part of?
serine protease family
describe structure of the serine protease active site (2 main components)
catalytic triad (aspartic acid, histamine and serine)
oxyanion hole
how does amide bond hydrolysis relate to cell walls?
describes the hydrolysis reaction that occurs as a part of the D-Ala-D-Ala peptide bond catalyzed by transpeptidase
describe the catalytic triad
part of serine protease
consists of 3 amino acids: aspartic acid, histamine, and serine
OH of serine is a nucleophile that reacts with amide carbonyl
Asp and His act together to form a base that deprotonates the OH of serine
what is the role of the oxyanion hole
stabilizes the negatively charged oxygen that is part of tetrahedral intermediate involved in amide bond hydrolysis
what does transpeptidase do in cross-link formation
essentially trims D-Ala from each peptide strand (either by H2O or amine)
what is the working part of penicillin? what does it do?
b-lactam (a 4-mem ring with an amide bond)
interacts with transpeptidase causing its ring to open up. this forms acyl-enzyme intermediate and inhibition of transpeptidase
why does the opening of the b-lactam ring inhibit transpeptidase?
transpeptidase does not fold around the drug the same way it folds around cross link precursor
therefore, the next steps of the reaction cannot proceed and transpeptidase enzyme is stuck with penicillin residue which inhibits cross link formation reaction
essentially, open-ring penicillin is part of the acyl-enzyme intermediate that is improperly folded, therefore further reactions cannot occur
what type of inhibition does penicillin use to inhibit transpeptidase?
covalent inhibition (a form of irreversible inhibition)
why is penicillin a good drug?
non-toxic, safe, few side effects
only targets bacteria cells (since humans do not have any enzyme equivalent to transpeptidase + do not have cell walls)
what causes penicillin allergies?
humans could randomly have a serine protease/other protein in body with a nucleophilic component
penicillin (an electrophile) could chemically interact with it (acylates it)
penicillin ring opens and forms an acyl protein intermediate that body recognizes as foreign which results in allergic reaction
why do penicillin allergies get stronger over time?
will get stronger because body will have built up antibodies
how are penicillin and transpeptidase similar? what does this allow for
penicillin has structure similar to D-Ala-D-Ala structure of transpeptidase + similar non covalent interactions
allows penicillin/transpeptidase to recognize each other, allowing for inhibition to occur
what are the two main forms of b-lactam + their characteristics
chain = difficult to work with
square cyclic form = easy to work with because b-lactam doesn’t want to be in the square form, so it easily pops out of it
what is penicillin G? what are its four limitations?
natural form of penicillin (isolated from penicillin mold)
limitations: acid sensitivity, resistance, spectrum of action, and bioavailability
why is acid resistance a problem with penicillin G? what two methods can solve?
if ingested orally, penicillin will be destroyed be acid in the stomach therefore is not orally available
therefore, penicillin G must be administered via injection only
describe two ways that can solve acid resistance of penicillin G (how to make it bioavailable)
add heteroatom (electron withdrawing group) to the left side of structure to reduce the nucleophilicity of the carbonyl oxygen
protonate (add charge) to the NH making it positively charged. at 7.4 it is a strong electron withdrawing group
overall - figure out way to add electron withdrawing groups
what is semi-synthesis?
the process of taking natural penicillin and modifying it to create other versions of the drug
why is the core of penicillin challenging to synthesize? what must be used instead?
because the core must be obtained from biological sources which could be difficult to gain access to
synthetic transformation must be used to prepare new drug
describe first part of synthesis of penicillin g
biochemical production of 6-APA
-grow penicillin mold and extract penicillin G from it
-use amides enzyme (from e coli) to remove side chain from pen G
-side chain (the core) is 6-APA which is then used to make other versions of the drug
what is the core structure used in semi-synthesis to make modified version of penicillin
6-APA
what is involved in the second step of the semi-synthesis of penicillin G
coupling reaction using peptide coupling reagents
DCC and carboxylic acid are mixed together to generate a large leaving group which then leaves
essentially a little group is added to the left side of the structure
how does bacteria develop a resistance to penicillin?
developing mutations in transpeptidase (changes in activate site)
evolving ways to get rid of drug (such as actively transporting out of cell, or destroying it)
how does b-lactamase aid in the resistance of bacteria against penicillin?
b-lactamase opens the b-lactam ring of penicillin (active area)
this makes it useless, so can no longer inhibit transpeptidase
how can the activity of penicillin be regained after resistance?
done using a shield: a large substituted heterocycle attached to the left side of penicillin
this makes penicillin no longer able to fit into the active site of b-lactamase, and can no longer be deactivated as a result
can still fit into active site of transpeptidase so that inhibition can still occur
what are two examples of penicillin modified for resistance?
oxacillin and methicillin
what are the two general types of bacteria? what type was the 1st penicillin effective against?
gram positive and gram negative
first penicillin only effective against gram positive
why could the original penicillin not kill gram negative bacteria?
gram negative has an additional lipopolysaccharide outer layer that acts as a protected barrier from penicillin
how can penicillin kill gram negative bacteria
by adding hydrophilic branched groups onto the left side
this allows for penicillin to have increased solubility in the outer layer of gram negative bacteria because it relates with the lipopolysaccharide layer (both fatty/greasy/hydrophillic)
allows penicillin to penetrate layer and kill the bacteria
ex. ampicillin
why is penicillin not being water soluble an issue?
makes it not bioavailable - must be administered via injection
poor intestine absorption
how can penicillin not being very water soluble be fixed
by protonating the NH2 group on the structure, giving a positive charge and increasing its water solubility/polarity as a result
what are prodrugs?
involve the addition of a removable group to improve the absorption of the drug into body
once drug is in the blood, the group is removed creating the active form of the drug
how do prodrugs increase bioavailability of penicillin
increase water solublility
ensuring that the molecule is charged at the bodily pH of 7.4
achieved by attaching removable group to the molecule that blocks one of the charged sites of the drug (often the carboxylic acid of penicillin)
what two molecules must be charged for prodrugs to work (and why)
NH3+ important for acid stability in stomach
CO2- necessary to fit into active site of transpeptidase
both provide temporary ways of blocking CO2
what are celaphalosporins
class of b-lactam antibiotics
originated from fungus in Italian sewer
what structural features are common to both penicillin and cephalosporins
b-lactam
what are the advantages of celaphalosporins?
lipophilic, so broad spectrum
[4,6] ring system less reactive than [4,5] which allows for reactivity against resistant strains of bacteria
lower risk of allergy
what are the disadvantages of celaphalosporins
not orally active
low potency therefore higher doses are required
what is the significance of the 7-ACA structure of celaphalosporins
reduced structure of the original drug
allows for its properties to be modified so better versions can be made
what is clauvulanic acid and where does it originate from
a type of b-lactam drug
originates from steptomyces clauvuligerus: a species of gram positive bacteria
not an antibiotic - so does not kill/inhibit transpeptidase
what is the main purpose of clavulanic acid?
destroys b-lactamase
forms a non-functional b-lactamase which is beneficial for antibiotics (so they won’t be destroyed/inhibited)
how is clavulinic acid used?
in combination with a b-lactam antibiotic that is affected by b-lactamase
the CA essentially inhibits the b-lactamase protecting the antibiotic from resistance
b-lactam antibiotic inhibits the transpeptidase and kills bacteria
what are drug-drug interactions?
occurs when one drug changes the bioavailability of another
maximizes or lowers the amount of drug
ex. grapefruit inhibition (can affect the effectiveness of drugs - can be dangerous)
what is vancomycin? and what is it produced from
produced from steptomyces orientalist bacteria
works to prevent cell-wall cross linking in bacteria
what type of drug is vancomycin? describe characteristics
glycopeptide drug
contains sugars and short protein (peptide) containing amino acids
also contains aromatic rings on the proteins (peptides) that are linked together forming a large bowl shapes structure
how does vancomycin prevent cell-wall cross linking in bacteria
binds strongly to the D-Ala-D-Ala of peptide chains
prevents transpeptidase from binding with tail end of cell wall pre-cross link chain
therefore, no cell wall will be formed
what type of inhibition is involved with vancomycin?
enzyme inhibition by substrate binding
inhibitor (vancomycin) binds to the substrate preventing transpeptidase with interacting to form the enzyme-substrate complex and peptide cross links from forming
what type of bacteria is vancomycin effective with
gram positive
because it is a large molecule that is not lipophilic enough to cross the lipopolysaccharide layer of gram negative bacteria
why is new antibiotic research limited
because lots of cheap and available antibiotics on the market
