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  <xsd:element name="DebtDetailsTable" id="sxtp_DebtDetailsTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="SmallBusinessAdministrationMember" id="sxtp_SmallBusinessAdministrationMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="BalloonPaymentMember" id="sxtp_BalloonPaymentMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="SBAMember" id="sxtp_SBAMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="DerivativeLiabilitiesDetailsTable" id="sxtp_DerivativeLiabilitiesDetailsTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="MilestonePayment" id="sxtp_MilestonePayment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element name="RoyaltyPercentage" id="sxtp_RoyaltyPercentage" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="duration" />
  <xsd:element name="ScheduleOfDerivativeLiabilitiesMeasuredAtFairValueOnARecurringBasisAbstract" id="sxtp_ScheduleOfDerivativeLiabilitiesMeasuredAtFairValueOnARecurringBasisAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="DerivativeLiabilitiesScheduleofDerivativeLiabilitiesMeasuredatFairValueonaRecurringBasisDetailsTable" id="sxtp_DerivativeLiabilitiesScheduleofDerivativeLiabilitiesMeasuredatFairValueonaRecurringBasisDetailsTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="ContingentMilestonePaymentMember" id="sxtp_ContingentMilestonePaymentMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="BridgeSharesMember" id="sxtp_BridgeSharesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisMarkToMarketAdjustment" id="sxtp_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisMarkToMarketAdjustment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element name="ShareBasedCompensationDetailsTable" id="sxtp_ShareBasedCompensationDetailsTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="TwoThousandTwentyTwoEquityIncentivePlanMember" id="sxtp_TwoThousandTwentyTwoEquityIncentivePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="StockOptionsMember" id="sxtp_StockOptionsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="SharesIssuedPayrollTaxesWithholdings" id="sxtp_SharesIssuedPayrollTaxesWithholdings" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="duration" />
  <xsd:element name="UnamortizedBalance" id="sxtp_UnamortizedBalance" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element name="ScheduleOfShareBasedCompensationExpensesAbstract" id="sxtp_ScheduleOfShareBasedCompensationExpensesAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="CommitmentsandContingenciesDetailsTable" id="sxtp_CommitmentsandContingenciesDetailsTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="CherylXuMember" id="sxtp_CherylXuMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="PaulFieldMember" id="sxtp_PaulFieldMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="CharlesAllenMember" id="sxtp_CharlesAllenMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="StephenTooveyMember" id="sxtp_StephenTooveyMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="USGovernmentSalesMember" id="sxtp_USGovernmentSalesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="USArmyAgreementMember" id="sxtp_USArmyAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="NumberOfNonAuditCommitteeChairs" id="sxtp_NumberOfNonAuditCommitteeChairs" type="xbrli:integerItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="instant" />
  <xsd:element name="LicensedTechnologyTerm" id="sxtp_LicensedTechnologyTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="duration" />
  <xsd:element name="AnnualRoyaltyPaymentPercentage" id="sxtp_AnnualRoyaltyPaymentPercentage" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="duration" />
  <xsd:element name="PercentageOfRoyaltyPaymentsOfNetSales" id="sxtp_PercentageOfRoyaltyPaymentsOfNetSales" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="duration" />
  <xsd:element name="PercentageOfTreatmentOfBabesiosis" id="sxtp_PercentageOfTreatmentOfBabesiosis" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="duration" />
  <xsd:element name="NumberOfExecutives" id="sxtp_NumberOfExecutives" type="xbrli:integerItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="instant" />
  <xsd:element name="SignificantCustomerTwoMember" id="sxtp_SignificantCustomerTwoMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="SignificantCustomerThreeMember" id="sxtp_SignificantCustomerThreeMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="TrevallyLLCMember" id="sxtp_TrevallyLLCMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="AgreedToReturnShares" id="sxtp_AgreedToReturnShares" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="duration" />
  <xsd:element name="July2025OfferingMember" id="sxtp_July2025OfferingMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="JulyTwoThousandTwentyFivePreFundedWarrantsMember" id="sxtp_JulyTwoThousandTwentyFivePreFundedWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="JulyTwoThousandTwentyFiveAOneWarrantsMember" id="sxtp_JulyTwoThousandTwentyFiveAOneWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="JulyTwoThousandTwentyFiveATwoWarrantsMember" id="sxtp_JulyTwoThousandTwentyFiveATwoWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="JulyTwoThousandTwentyFivePlacementAgentWarrantsMember" id="sxtp_JulyTwoThousandTwentyFivePlacementAgentWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="ProceedsFromIssuanceATMOfferingCosts" id="sxtp_ProceedsFromIssuanceATMOfferingCosts" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element name="ATMOfferingNetOfOfferingCostsPaid" id="sxtp_ATMOfferingNetOfOfferingCostsPaid" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element name="IssuanceOfCommonStockPursuantToATMOfferingNetOfOfferingCostsPaid" id="sxtp_IssuanceOfCommonStockPursuantToATMOfferingNetOfOfferingCostsPaid" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="duration" />
  <xsd:element name="StockIssuedDuringPeriodValueIssuanceOfCommonStockPursuantToATMOfferingNetOfOfferingCosts" id="sxtp_StockIssuedDuringPeriodValueIssuanceOfCommonStockPursuantToATMOfferingNetOfOfferingCosts" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element name="SeriesAWarrantsMember" id="sxtp_SeriesAWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="SeriesBWarrantsMember" id="sxtp_SeriesBWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="SeptemberTwoThousandTwentyFourAgentWarrantsMember" id="sxtp_SeptemberTwoThousandTwentyFourAgentWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="CommonStockAggregateOfferingPrice" id="sxtp_CommonStockAggregateOfferingPrice" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element name="ATMOfferingShares" id="sxtp_ATMOfferingShares" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="duration" />
  <xsd:element name="NumberOfDirectors" id="sxtp_NumberOfDirectors" type="xbrli:integerItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="instant" />
  <xsd:element name="HCWainwrightAndCoLLCMember" id="sxtp_HCWainwrightAndCoLLCMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="SeriesAAndSeriesBWarrantsMember" id="sxtp_SeriesAAndSeriesBWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="TuftsMedicalCenterAgreementMember" id="sxtp_TuftsMedicalCenterAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1Minimum" id="sxtp_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1Minimum" type="xbrli:durationItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="duration" />
  <xsd:element name="SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1Maximum" id="sxtp_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1Maximum" type="xbrli:durationItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="duration" />
  <xsd:element name="AtTheMarket2025AgreementMember" id="sxtp_AtTheMarket2025AgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="SalesAgreementTerminationDate" id="sxtp_SalesAgreementTerminationDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="duration" />
  <xsd:element name="CommonStockAggregateGrossSalesProceedAuthorized" id="sxtp_CommonStockAggregateGrossSalesProceedAuthorized" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element name="SalesAgentCommissionPercentage" id="sxtp_SalesAgentCommissionPercentage" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="instant" />
  <xsd:element name="ProceedsFromCommonStockSalesAgreementNet" id="sxtp_ProceedsFromCommonStockSalesAgreementNet" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element name="DirectorOneMember" id="sxtp_DirectorOneMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="AccountsReceivableOrSalesRevenueNetMember" id="sxtp_AccountsReceivableOrSalesRevenueNetMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="ValuationOfContingentMilestonePaymentDiscountRate" id="sxtp_ValuationOfContingentMilestonePaymentDiscountRate" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="instant" />
  <xsd:element name="UnamortizedBalancePrepaidAssets" id="sxtp_UnamortizedBalancePrepaidAssets" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element name="UnamortizedBalanceOfPrepaidAssetsRecognizedRatablyOverRemainingServicePeriod" id="sxtp_UnamortizedBalanceOfPrepaidAssetsRecognizedRatablyOverRemainingServicePeriod" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element name="UnamortizedBalanceOfPrepaidAssetsRemainingBalanceRecognizedAsResearchAndDevelopmentServices" id="sxtp_UnamortizedBalanceOfPrepaidAssetsRemainingBalanceRecognizedAsResearchAndDevelopmentServices" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element name="NumberOfTranches" id="sxtp_NumberOfTranches" type="xbrli:integerItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="instant" />
  <xsd:element name="AtTheMarket2026OfferingMember" id="sxtp_AtTheMarket2026OfferingMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="IncreasedCommonStockAggregateGrossSalesProceedAuthorized" id="sxtp_IncreasedCommonStockAggregateGrossSalesProceedAuthorized" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element name="ReverseStockSplitFractionalSharesRoundingAdjustment" id="sxtp_ReverseStockSplitFractionalSharesRoundingAdjustment" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="duration" />
  <xsd:element name="ConsultingAgreementMember" id="sxtp_ConsultingAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalGrantsEachMonth" id="sxtp_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalGrantsEachMonth" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="duration" />
  <xsd:element name="DescriptionConsultingAgreementTerm" id="sxtp_DescriptionConsultingAgreementTerm" type="xbrli:stringItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="duration" />
  <xsd:element name="January2025OfferingMember" id="sxtp_January2025OfferingMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="JanuaryTwoThousandTwentyFiveWarrantMember" id="sxtp_JanuaryTwoThousandTwentyFiveWarrantMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="ClassOfWarrantOrRightsExpiryTerm" id="sxtp_ClassOfWarrantOrRightsExpiryTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:periodType="duration" />
  <xsd:element name="JanuaryTwoThousandTwentyFiveAgentWarrantMember" id="sxtp_JanuaryTwoThousandTwentyFiveAgentWarrantMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="February2025OfferingMember" id="sxtp_February2025OfferingMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="FebruaryTwoThousandTwentyFiveWarrantMember" id="sxtp_FebruaryTwoThousandTwentyFiveWarrantMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="FebruaryTwoThousandTwentyFiveAgentWarrantMember" id="sxtp_FebruaryTwoThousandTwentyFiveAgentWarrantMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="March2026AtTheMarketAgreementMember" id="sxtp_March2026AtTheMarketAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="CommonStockAggregateGrossSalesProceedAuthorizedIncrease" id="sxtp_CommonStockAggregateGrossSalesProceedAuthorizedIncrease" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" abstract="false" xbrli:balance="debit" xbrli:periodType="duration" />
</xsd:schema>
